Glossary of Terms
Abrasive Wear- Wear caused by the continual contact, under pressure of hard particles in the resins against the barrel lining, screw and valve components. The abrasive particles may be fillers or reinforcements, such as fiberglass, calcium carbonate, powdered metals and others.
Additive - A substance compounded into a resin to modify its characteristics (i.e. intestates, stabilizers, plasticizers, flame retardants, etc.).
Adhesive Wear- Wear resulting from two metals rubbing against each other, such as the screw flight lands and valve rings coming into contact with the barrel lining during operation.
AGVS- Automatic guided vehicle system
Amorphous- A term describing polymers having no crystalline structure.
Anneal- To heat an article to a predetermined temperature and slowly cool it to relieve stresses. The annealing of metal components may reduce their hardness.
AS/RS- Automated storage and retrieval system
ASA- Acrylic-styrene-acrylonitrile
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B
Ball Check Valve- A device mounted at the discharge end of an injection screw used to allow forward flow of plastic during recovery and no flow during the injection stroke. This valving is accomplished by positioning of an internal ball.
Barrel (Cylinder)- A cylindrical housing in which the screw rotates, including the integrally formed special inner surface material, or replaceable liner, if used. Also commonly referred to as a cylinder.
Barrel Shell (Backing Material)- The outer thick wall of the barrel made from metal backing material to provide strength and to hold the lining.
Barrier Flight- A secondary flight of reduced outside diameter and usually designed to separate melted polymer from solid polymer or to enhance melting by having the polymer pass over it.
Bayonet Adapter- A cylindrical shaped part with holding pins that threads into the thermocouple hole and retains a spring loaded thermocouple.
Bearing (HUB)- The portion of the screw immediately behind the flighted length which prevents the escape of material and provides a seal between the screw and the barrel.
Bell End- A flange at the discharge end of the barrel which provides added strength to withstand internal pressure.
Bimetallic- A term used to indicate that a barrel is composed of two (or more) metals, commonly used to refer to barrels which have a centrifugally cast lining.
Blister Ring- A raised portion of the root between flights of sufficient height and thickness to effect a shearing action of the polymer as it flows between the blister ring and the inside wall of the barrel.
Blow Molding- A method of fabrication in which a warm plastic parison (hollow tube) is placed between the two halves of a mold cavity and forced to assume the shape of that mold cavity by the use of air pressure. Pressurized air is introduced into the inside of the parison through a blow pin thereby forcing the plastic parison against the surface of the mold that defines the shape of the product.
BMC- Bulk molding compound
Bore- The inside diameter of the barrel which houses the screw.
Breaker Plate (Extrusion)- A metal plate installed across the flow of the melt between the end of an extruder screw and the die adapter with openings through it such as holes or slots. It commonly supports a screen and also reduces any swirling in the melt flow before it reaches the die.
Breaker Plate Recess (Extrusion)- The internal counterbore at the discharge end of an extruder barrel that accepts the breaker plate and provides the seal and alignment of the die adapter.
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C
"C" Clamp Flange- A circular tapered flange at the discharge end of an extruder barrel used to hold the die adapter. A similar shaped flange on the die adapter and a "C" shaped clam accomplishes the closure.
Channel- With the screw in the barrel, the space between the flights bounded by the root of the screw and the bore of the barrel.
Channel Area (Axial)- The cross-sectional areas of the channel measured in a plane through and containing the screw axis.
Channel Depth- The distance in a radial direction from the bore of the barrel to the root of the screw.
Channel Volume- The volume developed by the "axial area o f screw channel" in one revolution about the screw axis. The location of measurement should be specified..
Channel Volume (Enclosed)- The volume of screw channel starting form the forward edge of the feed opening to the discharge end of the screw channel. Also called screw inventory.
Channel Width- The distance across the screw channel in a direction perpendicular to the flight measured at the periphery of the flight.
Check Ring- The cylindrically shaped component of a non-return valve that reciprocates in an axial direction. During injection, the ring shuts off against the surface of the rear seat of the valve preventing the melt from flowing backward toward the feed section of the screw. During screw recover, the ring rests against the front seat (or stud in a three piece valve) of the valve allowing melt to flow forward through the valve to the discharge end of the barrel.
Clearance (Screw/Barrel)- The difference in the diameters of the screw and the bore (diametral clearance) or, more commonly, one-half the diametral clearance, referred to as radial clearance.
Coefficient of Thermal Expansion- The fractional change in dimension (sometimes volume) specified of a material (plastic, metal or other materials) per a unit change in temperature.
Color Concentrate- A measured amount of die or pigment combined into a predetermined amount of resin, serving as a carner to for a color concentrate. The concentrate is then added to the bulk of the resin in measured quantity to achieve a predetermined color in the finished plastic product.
Compression Ratio (Channel Depth)- The factor obtained by dividing the channel depth in the feed section of the screw by the channel depth in the meter section (or the depth of the last complete flight). This Channel Depth ration is commonly referred to as the Compression Ratio. In constant lead screws this value approximates, but is greater than the volumetric compression ratio.
Compression Ratio (Volume)- The factor obtained by dividing the developed channel volume of the screw at the feed opening by the developed volume of the last full flight prior to discharge. This is not the commonly used definition of compression ratio (see Compression Ratio - Channel Depth)
Compression Section- See Transaction Section
Concentricity- The term to describe two circles or cylindrical shapes having a common center and common axis, such as the inside and outside diameters of the flighted surface and bearing surface of a screw. Deviation from concentricity is referred to as "Runout".
Conical Transition- Transition where the depth charge is accomplished with a conical shaped root surface (interrupted by the screw flights).
Core- An internal hole extending longitudinally from the shank through a portion of the screw for the circulation of a heat transfer medium or installation of a heater.
Corrosive Wear- Wear caused by the attack of various acids on the surface of screws, barrels, valves and other processing components. Acids formed in the processing of plastic erode and pit the metal surfaces. The acids come from the polymers themselves or from flame retardants, forming and coupling agents.
Counterbore- The recessed area in the discharge end of an injection barrel which acts as a pilot to assure the concentric fitting and seal surface of the end cap to the barrel.
Crystallinity- A state of molecular structure in some polymers that denotes uniformity and compactness of the molecular chains forming the polymer.
Cycle- The complete, repeating sequence of operations in a process or part of a process. In molding, cycling time is the elapsed time between a certain point in one cycle and the same point in the next.
Cylinder- See Barrel
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D
Diameter (Barrel)- The nominal inside diameter of an extrusion or injection barrel. See Bore.
Diameter (Screw)- The nominal outside diameter of a screw. See Flight Land.
Die- The metal orifice mounted to the discharge end of a extruder barrel through which the melt flows to form a desired extrudate. Commonly includes the die block and die adapter which holds the die block.
Die Adapter- Part of an extruder die which holds the die block.
Die Block- Part of an extruder die which contains the orifice through which the melt flows to form an extruded product.
Dispersive Mixing- The mixing of a fluid (melted polymer) with a solid (unmelted polymer, pigment and agglomerates above a certa size, etc.) which exhibits a yield port. Dispersive mixing is involved in the final melting of a polymer or breaking down a pigment in the manufacture of a color concentrate.
Distributive Mixing- The mixing of a fluid (melted polymer) and other components (such as liquid color concentrate) where all components are fluids and do not exhibit a yield point. Distributive mixing is aimed at achieving thermal and color uniformity where no solids breakdown is required.
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E
Endcap- The device that bolts to the discharge end of an injection barrel and adapts the injection nozzle.
Endcap Bolts- The bolts used to attach the endcap to the injection barrel.
Extrudate- The stock or melt as it emerges from the discharge orifice (die) in a desired product form, such as film, pipe, coating on wire and others.
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F
Feed Housing- A separate components of an extruder barrel assembly which contains the feed openings, water cooling channels and, in some cases, a grooved interior lining. It is capable of withstanding high pressures (15,000 PSI or more), especially if it is grooved, and may incorporate a thermal barrier between it and the barrel to which it is attached. Also referred to as feed throat.
Feed Opening- A hole through the feed section of the barrel for the introduction of feed material into the barrel. Also referenced to as feed hole or feed port.
Feed Port- See Feed Opening
Feed Section (Screw)- The portion of the screw which receives the material to be processed and conveys it to the transition section of the screw. The feed section normally has a constant channel depth and constant root diameter.
Filler- An insert substance added to plastics for the purpose of improving physical properties or process ability, or to reduce the cost of material.
Flange- A short external section of the barrel, with a large diameter, through which bolt holes have been placed to either assist in mounting the barrel to the machine, or to which an end cap, die adapter or other member is fastened. It may also add strength to that section of the barrel.
Flight- The helical metal thread or raised portion of the screw.
Flight Angle- See Helix Angle.
Flight Cutback- The portion of the screw at the discharge end that is not flighted. This is normally included for calculations as part of the flight length.
Flight Depth- The distance in a radial direction from the land of the screw flight to the root.
Flighted Length- Overall axial length of the flighted portion of the screw, from the start of the feed pocket to the front end of the register or (in the case of extruder screws or smear head screws) the point where the mot diameter begins to decrease. Flighted length does not include valves.
Flight Face- The face of the flight extending from the root of the screw to the flight land. The rear face is the side toward the feed section and the front face is the side toward the meter end of the screw.
Flight Hard Surface- A screw flight having its periphery harder (or more wear resistant) than the base screw metal achieved by flame hardening, induction hardening, heat treating, depositing of hard facing metal, or other means.
Flight Land- The surface at the radial extremity of the flight constituting the periphery or outside diameter of the screw.
Flight Land Width- The distance across one flight land in a direction perpendicular to the flight. Commonly referred to as flight width.
Flight Lead- The distance in an axial direction from the center of a flight land to the center of the same flight land after one complete turn. This is not flight pitch in a mufti-flighted screw.
Flight Pitch- The distance in an axial direction from the center of a flight land to the corresponding point of an adjacent flight land.
Front Radius- The radius at the intersection of the front or pushing side of the flight and the screw root. Usually this radius is smaller than the rear radius and may change from one portion of the screw to another.
Front Seat (Valve)- A separate wear resistant component of a non-return valve that limits the forward travel of the check ring.
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G
Grooved Liner (Or Barrel)- A liner whose bore is provided with longitudinal grooves, usually for several diameters in the feed section only.
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H
Heater Bands- The electrical heating elements mounted on or around the barrel, adapters, dies. nozzles! etc.
Heating Zone- A portion of the barrel length having independent temperature control of the heater bands.
Helix
Angle- The angle of a screw flight at its periphery
relative to a plane perpendicular to the screw axis.
It is calculated as: Helix Angle = Arctangent ( Lead) Pi x D)
Hopper (Feed)- A funnel-shaped container mounted directly on the barrel over the feed opening to hold a reserve of material to be processed.
Hygroscopic- A term applied to polymers in their pellet or powder form indicating a tendency to absorb moisture from air.
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I
Injection Pressure- The pressure of the injection screw against the melted plastics material (expressed in PSI), excluding any loss of pressure due to frictional drag of the screw, equal to the force acting upon the injection piston.
Injection Rate- The injection rate is the calculated rate of displacement of the screw (or plunger), expressed in cubic inches per second, computer at the injection pressure specified.
Inlay- A hard surface portion of a flight land not extending across the full flight width.
Involute Transition- The transition where the depth change is accomplished with a root surface which remains parallel to the screw axis but changes its depths.
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L
L/D Ratio (Screw)- The ratio of the working flighted length of the screw (distance from the front edge of the feed opening to the forward end of the screw flight when the screw is in the forward position) to Its outside diameter. In practice, the ratio calculation is simplified to dividing the flighted length of the screw by its nominal diameter.
Lead (Screw)- The distance measured parallel to the screw axis from one edge of the top of a screw flight to the same edge of the same flight after one complete turn. It is not the distance measured to the next screw flight in a multiflighted screw. (For this see PITCH)
Liner- The wear resistant removable sleeve(s) in the barrel.
Lining- The internal wear resistant portion of an extrusion or injection barrel. The lining may be metallurgically bonded to the inside diameter of the barrel shell or be removable liners that are press or shrink fit into the barrel shell bore.
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M
Melt- Plastic material in a molten condition.
Melt Channel- The channel in a barrier screw designed to collect and convey forward the melted polymer.
Metering Section- The portion of the screw at the discharge end with a constant flight depth and having a length of at least one turn of the flight.
Mixing Section- An area of the screw with special geometry designed to enhance -distributive and/or dispersive mixing in the melted polymer.
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N
Nitriding (Gas)- The surface hardening of certain alloy steels by heating the steel in an atmosphere of nitrogen (ammonia gas) at approximately 9500F. A very hard (70+Rc) case depth of .007" to .0 15" results which is wear resistant. Process is commonly used for barrel inside diameters, screws and valve components.
Nitriding (ION)- The surface hardening of certain alloy steels by heating the steel (to approximately 600 OF) in an atmosphere of hydrogen gas, adding an electrical charge to the steel and nitrogen gas, allowing a bombardment of the positively charged steel by hydrogen and nitrogen gas ions. This creates a hard (70+Rc) wear resistant, case hardness to a slightly greater and more uniform depth than gas nitriding with less distortion or contamination of the workpiece. Process is commonly used on screws and valve components.
Non-Return Valve- A device mounted at the discharge end of an injection screw that uses a sliding ring to allow flow of plastics in one direction only. On screw recovery it allows flow forward. On injection stroke it allows no flow and makes the screw perform like a plunger.
Nose Cone- The conical surface at the discharge end of an extrusion screw.
Nozzle- A device that threads into the endcap and adapts the nozzle tip to the endcap.
Nozzle Tip- A device that threads into the injection nozzle and adapts between the nozzle and the sprue bushing of the injection mold.
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O
Overall Length (Screw)- The total length of the screw parallel to the screw axis. It includes the flighted length, the shank and any nose cone, but not the non-return valve.
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P
Parison- The hollow tube of molten polymer which is pinched at one or both ends and inflated in a blows mold to make a hollow part. See Blow Molding.
Pilot (Barrels)- A cylindrical portion at the rear end of an extruder barrel used to locate the barrel with the feed throat.
Pilot (Screws)- An internal cylindrical surface at the front end of an injection screw used to accurately locate a non-return valve or other portion that attaches to the screw.
Pitch- The distance measured parallel to the screw axis from one edge of the top of the screw flight to the same edge of the adjacent flight. In the case of a mufti-flighted screw the pitch is less than the lead.
Plasticizing Capacity- The maximum quantity of a specified plastic material that can be raised to a uniform and moldable temperature in a unit of time. This capacity is generally expressed in pounds per hour (or ounces per second) as calculated from the recovery rate.
Pocket- A place where a screw flight is initiated, usually starting from a cylindrical area or another flight. A feed pocket exists on most screws and is located at the intersection of the bearing and the beginning of the flight.
Polymer- A high-molecular weight organic compound, natural or synthetic' whose structure can be represented by small repeat units (monomers) forming chemical bonds with the same or other monomers. If two or more monomers are involved, a copolymer is obtained.
Press Fit- An interference fit, characterized by constant bore pressure throughout, achieved by mechanically forcing the entering piece into the receiving piece by use of a press or similar machine. Barrel liners may be press fit into the prepared barrel shell.
Pressure Tap- A hole designed to accept a pressure transducer or pressure gauge.
Pump Ratio- The ratio obtained by dividing the depth of the second metering section by the depth of the first metering section on a two-stage screw.
Pushing Side- The flight face of the screw flight that faces the discharge end and runs from the front radius to the top of the flight land. This surface is commonly close to being perpendicular to the axis of the screw.
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R
Raised Register- A register that has a larger diameter than the adjacent root diameter. This is sometimes supplied on injection screws having metering depths too deep to match the rear seat of a standard non-return valve.
Rear Radius- The radius at the intersection of the rear or trailing side of the flight and the screw root. Usually this radius is larger than the front radius and may change from one portion of the screw to another.
Rear Seat- A flat, ring shaped portion of a non-return valve that abuts the front vertical face of an injection screw and seals the flow of plastic by contact with the rear conical shaped end of the check ring.
Recovery Rate- The weight (or volume) of a specified moldable material discharged from the screw per unit of time, when operating at 50% of injection capacity, as determined by SPI test procedure. The rating is normally expressed as ounces r cubic inches) per second.
Register- The cylindrical portion of an injection screw at the most forward end accurately machined to match the rear seat of the non-return valve.
Relief- An area of the screw shank of lesser diameter than the outside diameter and located between the bearing and the spline or keyway.
Resin- Any of a class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point. In the broadest sense the term is used to designate any polymer that is a basic material for plastics. Most resins are polymers.
Retainer- The larger part of a no n-return valve that threads into the injection screw. The forward portion retains the front seat or the sliding ring. The front end of the retainer is usually torpedo or conical shaped and usually is fluted.
Ring (Valve)- See Check Ring.
Rockwell Hardness- A common method of expressing the degree of hardness of a material by testing its resistance to indentation, under pressure, by a diamond or steel ball. Results are expressed on various scales, the most common of which is the "C" scale, identified as Rc, which is used to compare the hardness of barrel linings, screw surfaces and valve components. A similar test, Brinnell hardness test, expresses results on a somewhat different scale and is identified as HB.
Root- The surface of the screw between the flights, usually a cylindrical or conical shape, of a diameter smaller than the outside diameter of the flights.
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S
Screen Pack- A woven metal screen or equivalent device installed across the flow of melt between the tip of an extruder screw and the die and supported by the breaker plate. It is used to strain out contaminants or to increase the back pressure or both.
Screw- A helically flighted shaft which rotates within the barrel to mechanically work and advance the material being processed.
Screw Axis- A reference line of infinite length drawn through the center at the rear of the shank and the center of the discharge end.
Screw Channel- See Channel.
Screw Diameter- The dimension defined by the cross-section of the screw bounded by its flight lands. Although it is usually expressed as a nominal diameter (such as 3 1/2") its actual diameter could be 3.490" to 3.492".
Screw Inventory- See Channel Volume (Enclosed)
Screw Speed- The number of screw revolutions per minute (RPM).
Sealing Ring- A round ring used in place of a breaker plate to seal between an extruder b barrel and the die adapter.
Shank- The non-flighted portion of the screw at the drive end.
Shear Ring- See Blister Ring.
Shot.- The yield from one complete Injection molding cycle, including the part, runner systems and flash.
Shot Capacity- The maximum volume of material which an injection molding machine can produce from one forward motion of the screw. Commonly expressed in ounces.
Shrink Fit- An interference fit, characterized by a constant bore pressure throughout, achieved by heating the larger receiving piece to allow the smaller mating piece to enter. In some cases, barrel liners are shrink fit into the prepared barrel shell. See also Press Fit.
Sleeve- See Liner.
Smear Tip- A conical device used in place of a non-return valve at the discharge end of an injection screw. This smear tip is generally used with high viscosity, heat sensitive materials where a non-return valve would cause degradation.
Solids Channel- The channel in a barrier screw that is connected to the feed channel and is designed to contain and convey forward unmelted polymers.
Square Pitch- A screw flight where the pitch is equal to the nominal screw diameter, i.e., 3 1/2" diameter screw with a 3 1/2" lead
Surging- A pronounced fluctuation in extruder output over a short period of time without a deliberate change in operating conditions.
Swing Gate- A hinged device mounted at the discharge end of an extruder barrel and used to support the die adapter.
Swing Gate Flange- A flange at the discharge end of an extruder barrel using bolts to attach the die adapter to the barrel.
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T
Thermocouple- A device, consisting of two dissimilar metallic conductors in contact. that produces an electrical current whose magnitude depends upon the temperature of the junction. The resulting temperature measurement feeds into a pyrometer to help monitor and control the temperature of a barrel or nozzle. The thermocouple is housed in a steel tubing adapter.
Thermocouple Hole- A machined hole in a barrel, nozzle or adapter designed accept the thermocouple adapter.
Thermoplastic- A material that will repeatedly soften when heated and harden when cooled. Typical thermoplastics are the styrenic polymers and copolymers, acrylics, cellulosics, polyethylene, polypropylene, vinyl's, nylons and various fluorocarbon materials.
Thermoset- A material that changes as a result of a chemical reaction to heat and pressure, catalysts or ultra-violet light, from a soluble, fusible stage to an insoluble infusible and cured condition. Typical thermoset materials are unsaturated polyesters (BMC), aminos (melamine and urea), alkyds, epoxies and phenolics.
T.I.R.- An abbreviation used to identify tolerances with respect to concentricity. Total indicator Reading is standard terminology for drafting and machinist work to describe the deviation in concentricity of a measured surface from a selected surface as shown on a dial Indicator. Also known as F.I.M. (Full Indicator Movement).
Torpedo- See Nose Cone.
Trailing Side- The flight face of the screw that faces the feed end and runs from the rear radius to the top of the flight land.
Transducer- A device for transferring power generated in one system to another system. Various types of electronic transducers are used in connection with molding and extruding equipment to measure, monitor and/or control linear position, pressure, temperature, speed and other factors. See separate MCMD publication covering Electronic Transducers Used By the Plastics Industry.
Transition Section- The portion of the screw between the feed section and the metering section in which the flight depth decreases in the direction of discharge. This section is sometimes referred to as the compression section.
Twin Barrel- A dual cylindrical housing in which two extruder screws rotate side-by-side, including a nitrided inner surface or a centrifugally cast bimetallic lining for resistance to wear. There are two major types of twin barrels: one, which provides for the intermeshing of the two extruder screws and; a second, in which the two extruder screws do not intermesh. Intermeshing, counter-rotating twin screw extruders are commonly used in profile extrusion of thermally sensitive materials, such as PVC. Intermeshing and non-intermeshing, counter and co-rotating twin screw extruders are used in a variety of specialty polymer processing operations.
Two-Piece Barrel- A cylindrical housing in which the screw rotates, that is construction of two sections. One section, which extends the full length of the varrel, consists of an outer shell (typically constructed of annealed alloy steel) with a full outside barrel diameter over the majority of its length, then tapering abruptly to a much smaller diameter over the final one-fourth (approx.) of As length at the discharge end of the barrel. This section commonly has a centrifugally cast, bimetallic lining for resistance to wear. The second section, is an outer shell with full outside barrel diameter (construction of heat treated alloy steel), which is shrink fit over the smaller diameter of the first section and welded to the larger diameter of that section at its taper area. The second section provides added yield strength to the barrel at its discharge end.
Two-Stage Screw- A screw for a vented barrel consisting of a feed, transition and meter section, followed by a decompression section (or vent section) located under the vent to allow the escape of volatiles without vent bleed. The decompression section has a deep channel and is usually several diameters in length, followed by a second transition and meter section. Frequently, two-stage screws are longer (24 to 32:1 L/D) than standard screws, although two-stage screws may be as low as 20:1 L/D.
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V
Vent Bleed- The unplanned escape of melt through the vent during the operation of vented barrel processing.
Vent Deflector- A barrel with a vent which utilizes a two-stage screw to accomplish the removal of volatiles from the material being processed.
Vent Hole- See Vent Port
Vent Port- An opening through the barrel wall, intermediate in the injection or extrusion process, to permit the removal of air, water vapor and volatile matter from the material being processed.
Vent Stack (Chute)- A device surrounding a major portion of the vent deflector designed to prevent any material that might escape through the vent port during start up from collecting on the barrel, heater bands or wiring.