Attachment and Specialty Roller Chains: Hollow Pin, Extended Pin and Custom Attachments for Conveyor Builders

Conveyor builders almost never fail because they picked the wrong size of transmission chain. They fail because the part that actually touches and carries the product — the plate, the pin extension, the cross rod, the pusher — was specified as an afterthought. A chain listed at twenty kilonewtons of minimum tensile strength tells you very little about whether a bent plate riveted to its side survives six months of start-stop indexing with a twenty kilogram load hanging two centimetres off the pin centreline. This article is written about that second half of the specification: the attachment structure itself, how it is named, how it is fixed to the chain, how much load it can honestly carry, how it is inspected, and what it costs to have it built your way.

What follows assumes you already understand standard transmission roller chain and now have to convert that knowledge into a conveyor specification. Where an application matters it is referenced only because it changes a structural decision, not because the application is the subject.

Attachment and Specialty Roller Chains: Hollow Pin, Extended Pin and Custom Attachments for Conveyor Builders

An attachment roller chain is a standard roller chain with regularly spaced features added so the chain can carry, push, index, locate or lift a product rather than simply transmit torque between two shafts. Those features may be formed into the link plate itself, riveted on as a separate piece, or created by extending the pin beyond the normal width of the chain. Each option changes how load enters the chain, and each one moves the failure point away from the classic pin-and-bushing wear mode that every standard chain life calculation assumes. Once you specify an attachment, you are designing a small machine part, not buying a catalogue commodity.

Standard Chains Versus Attachment Chains: Definition and Naming Rules

The distinction is simple on the surface. A standard chain has pin, bushing, roller, inner plate and outer plate, and its whole job is to sit in a sprocket and pull in a straight line along its own centreline. An attachment chain adds a geometry that transfers a load into or out of the chain at right angles to that line, or at some offset from it. That offset is the entire problem. The moment load enters off-centre it becomes a bending moment on a plate or a pin, and fatigue, not tensile strength, becomes the governing failure mode.

How the ANSI number encodes construction

The base designation follows the familiar rule: the number encodes pitch in eighths of an inch, so 40 is half inch pitch, 60 is three quarter inch pitch, 80 is one inch pitch, and the dash number records strand count, so 60-1 is single strand and 60-2 is double strand. A letter such as H flags a heavy series with thicker link plates and higher ultimate strength for the same pitch. Pitch is only half of what you need to name a chain, though. Roller diameter, inner width between inner plates, pin diameter, plate height and plate thickness are equally part of the identity, and they are exactly where interchangeability arguments start.

What 1R and 2R actually mean

In many supplier catalogues you will see single strand and double strand written as 1R and 2R. The digit is the strand count and the R is generally understood as riveted construction, distinguishing a permanently riveted assembly from a cottered or slip-fit variant built on the same base dimensions. Buyers should be careful here, because letter usage is not uniform: some makers use R purely as a formatting convention, some use it to mark a specific pin-end treatment, and ISO and GB literature may express the same idea with different letters entirely. The reliable approach is never to order on a suffix alone. Put the full dimensional string on your drawing and ask the supplier to confirm it line by line.

The attachment itself is rarely covered by the base standard

This is the point that catches most first-time buyers. Pitch, roller diameter and width are standardised. Attachment plate dimensions generally are not. Two manufacturers building a nominally identical 60-1 with a one-hole straight attachment may differ in plate thickness, hole centre height above the pitch line, hole diameter, edge distance and therefore usable strength. If you plan to source from more than one factory, freeze the attachment geometry in your own drawing rather than relying on a part code.

Base chain dimensions come from the standard; attachment plate geometry comes from the maker.
A part number is a shorthand, not a specification — the drawing is the specification.
Always record hole height above the pitch line, hole diameter and edge distance, not merely the hole count.

The Common Attachment Families

A-1 and K-1: straight and bent plates

The most widespread naming convention treats A as a straight plate running parallel to the chain centreline and K as a bent plate that rises away from it, with the trailing digit counting holes. So an A-1 carries one hole in a flat plate projecting from one side of the chain, and an A-2 carries two. A K-1 and K-2 follow the same logic in a bent form, letting you pick up load higher above the pitch line or reach across a frame member. Two-hole plates are not simply stronger versions of one-hole plates: the second hole resists the rotation that a single fastener allows, which is usually the real reason a single-hole attachment works loose.

Extended pin chains

When you want the attachment to pivot relative to the chain, or you need to hang something directly on the pin rather than on a plate, you extend the pin. The extension becomes a cantilever loaded shaft, so its root — at the outer face of the outer plate — sees the highest bending stress in the whole assembly. Anything you mount there behaves like a lever on that root, which is why every extended pin load rating has to be quoted together with its lever arm.

Hollow pin chain and cross rods

Take away solidity and replace the pin with a through-bored tube and you gain something no other family offers: a transverse axis you can push a rod through. This is the foundation of slat, apron and flight constructions where the cross rod carrying the slats becomes the structural spine. It also means the pin’s internal bore is now a wearing surface and must be treated as one.

Double-sided wing plates and tall plates

A wing plate protrudes from both sides of the chain simultaneously, which lets a load sit symmetrically over the pitch line and cancels much of the overturning moment that a one-sided plate creates. Tall or deep plates raise the load point, useful when the product must clear a rail or a sensor bracket, but every extra millimetre of height increases the bending arm.

Hollow Pin Chains in Detail: Fixing the Cross Rod

A hollow pin is a bushing-like tube with an accurately controlled bore and outer diameter, and the rod passing through it is either fixed to the chain and free to turn in the slat, or fixed to the slat and free to turn in the bore. Whichever way you choose, one interface is a bearing and one is a clamp, and the design must be explicit about which is which.

Cross rod retention methods

Interference press fit into the bore: simplest, permanent, relies entirely on bore tolerance and surface finish.
Split or coiled spring pin driven through the pin wall and rod: standard for hollow pin conveyor applications where field replacement matters.
Grooved pin with external circlip: positive location, but the groove weakens the tube wall and must be accounted for.
Threaded rod with nylon-insert nuts and washers: adjustable and serviceable, but the threads are a stress riser and a fretting site.
Collar and set screw on the protruding rod ends: cheap and quick, poor under reversing load because set screws relax.
End plate or cotter through a cross-drilled hole: very positive, restricts rod rotation unless intentionally slotted.

Tolerance and the clearance window

The rod-to-bore clearance is a genuine engineering compromise. Too tight and assembly stops being an assembly operation and becomes a press operation, with galling risk and permanently damaged rods every time a slat has to be replaced. Too loose and every reversal of load becomes a small impact, which rapidly ovalises the bore and introduces timing error between the two strands of chain running either side of the conveyor. In practice the clearance should be quoted explicitly on the drawing as a fit class, not left to the last operator who machined the rod. Record the target bore grade, target shaft grade and the resulting diametral window, then hold it with plug gauges at incoming inspection.

Wear inside the bore

The bore is the least lubricated bearing in the machine. It receives whatever oil survives the main joint, it sits directly above the product where contamination is worst, and it is often inaccessible. Standard practice is to treat the rod as sacrificial: hard chrome plated or through-hardened steel that can be pulled and replaced, protecting the far more expensive chain. Alternatively specify bore wear sleeves or polymer bushings that absorb the wear and can be renewed without touching the chain. Whichever route you take, define the rejection limit in the maintenance manual — typically an ovality or diametral growth figure at which the joint is considered out of tolerance, because rod deflection under load is the visible symptom of bore wear long before the chain looks worn anywhere else.

Rated Load versus Real Load on Extended Pins and Bent Plates

Chain catalogues quote minimum ultimate tensile strength, sometimes average tensile strength, and occasionally a maximum allowable dynamic load. None of those describes what an attachment will carry. Tensile strength is generated along the axis of the chain. An attachment load arrives perpendicular to it, applied at a distance, and produces bending in the plate neck and prying on the joint.

Converting-rated load to an attachment allowable

The only honest number comes from the manufacturer’s attachment load table, which is derived from testing done with a defined load geometry. Ask for it and ask what the test geometry looked like — cantilever length, load direction, static or cyclic. If no table exists, the conservative route is to take the allowable load of the attachment as a defined fraction of the chain’s own allowable dynamic load and then multiply by additional service factors. The distance between the load application point and the plate root or pin root is what makes or breaks the result, because allowable moment is fixed and allowable force is merely moment divided by arm length.

Derating factors to apply

Shock and start-stop duty: apply a service factor in the 1.2 to 1.5 range, higher if the drive has no soft start.
Load sharing between strands: two strands never share perfectly. Assume something meaningfully less than double the single-strand figure when alignment depends on the slat itself.
Cyclic versus static: calculate against fatigue for anything exceeding a modest number of full-load cycles per shift.
Temperature: derate both base strength and any plating or polymer components as temperature climbs.
Load eccentricity: any load applied outboard of the plate centreline twists the plate and should be derated further.
Moment reversal: alternating up-down loading is dramatically worse than one-directional loading of the same magnitude.

Tip: never read a chain’s catalog tensile strength as the allowable attachment load; demand the attachment-specific rating and its test geometry, then apply your own service factor on top of it.

How Attachments Are Fixed to the Chain

The fixing method determines whether an attachment can be replaced, whether it can rotate, and how much residual stress the joint carries.

Integral formed plate

The attachment is part of the outer plate, formed in one operation. This is the strongest and stiffest option because there is no joint to work loose, and it is the default for high-cycle conveyors. Its cost is that the plate geometry is committed early and changing it means new tooling.

Riveted-on separate plate

A separate plate is attached to standard outer plates by rivets through dedicated holes. Distortion control during riveting matters: too much squeeze and you distort the inner width and bind the joint; too little and the plate rotates under load.

Cotter pins, split pins and circlips

Used mainly on extended pins and cross rods. They give removability, cost almost nothing, and need a positive retention feature such as a groove or cross hole. Their weakness is that they retain axially but do not stop rotation, so a rotating pin is still possible unless the mating part is keyed or double-holed.

Secondary machining

Drilling, tapping, counterboring, milling flats and slotting are routine on attachment plates. Welding is the exception and should generally be avoided on hardened plates: the heat affected zone destroys the local heat treatment and creates a guaranteed crack initiation point at the edge of the weld. If a stainless bracket or bucket must be joined to a carbon steel plate, bolt it using existing holes or add a mechanically fixed machined adaptor.

Interchangeability: Pitch, Roller Diameter, Strand Count and Interference

Same pitch does not mean interchangeable, and the buyer who swaps a supplier on that assumption is the buyer who gets a call about noise in two weeks. Roller diameter must match the sprocket tooth form, inner width must clear the tooth thickness, plate height must clear the tooth tip, and the transverse pitch between strands must match a multi-strand sprocket exactly.

Interference checklist before you release a drawing

Roller outside diameter against the sprocket root radius and tooth flank on the smallest sprocket in the machine.
Attachment plate height against the sprocket tooth tips during wrap, worst case being a small sprocket with few teeth.
Adjacent attachments at minimum wrap radius — plates can collide long before the pins do, because the plate tips sweep a longer chord.
Attachment sweep against guide rails, wear strips, sensors, frame gussets and the product itself.
Cross rod ends and their fasteners against side frames and drive guards.
Total pin length and plate projection against the shaft, bearing housings and any idler with a flanged hub.
Free articulation: every joint must hinge freely through the wrap without the attachment striking the neighbouring link.
Catenary and return path: some return configurations place the attachment in tension against the product side.

Chain elongation compounds all of the above. Because each joint permits a small increase in effective pitch, the cumulative pitch error grows and attachments index progressively later than expected. A formal attachment interference check performed against the smallest sprocket in the machine catches this before it becomes a jam.

Materials and Heat Treatment for Attachment Chains

A roller chain is a deliberately mismatched assembly: the parts that must resist wear are hard, the parts that must survive impact are tough, and no single material satisfies both.

Component combinations

Link plates: medium carbon or manganese alloy steel, quenched and tempered to give high tensile strength with enough ductility to absorb shock without cracking at the hole edge.
Pins: low alloy steel, carburised or carbonitrided so the surface is hard for wear while the core stays tough enough to resist bending and shock.
Bushings: carburised, the primary wear partner of the pin.
Rollers: hardened to resist sprocket tooth impact, sometimes intentionally softer than the bushing so the cheaper part wears first.
Hollow pins: the hardest requirement of all, because the bore must resist fretting against the rod while the outside performs the normal pin duty.

Stainless and coated options

Stainless constructions are available for food, beverage and pharmaceutical environments where washdown chemistry rules out carbon steel. Remember that stainless has notably lower tensile and fatigue strength than hardened carbon steel, so a swap is almost always a size increase, not a like-for-like substitution. Plated and conversion-coated finishes — zinc, nickel, zinc-aluminium flake coatings plus lubricant top films — add corrosion resistance, but hydrogen embrittlement is a real hazard on carburised and hardened parts. Require post-plating baking whenever the part hardness exceeds the accepted threshold, and specify plating thickness for features such as rivet heads where dimensional clearance is tight.

The Custom Attachment Workflow

What the drawing must contain

Base chain dimensions: pitch, roller diameter, inner width, pin diameter, plate height and thickness.
Attachment geometry: plate length and height, section thickness, bend radius and angle, hole diameter and tolerance, hole location dimensioned from the pin centre datum, edge distances.
Spacing: attachment every link, every two pitches, or a repeating pattern, plus the total count per assembly length.
Fit requirements: bore and shaft grades for hollow pin versions, permitted clearance, retention method.
Material, hardness, case depth, plating type and thickness.
Load case: magnitude, direction, application point, cycles per hour, duty cycle, ambient and product temperature.
Datums and measurement method so inspection is repeatable between your team and the factory.

Sample fit-up

A drawing cannot validate interference. Fit the sample to the actual machine, with the actual sprockets, rails and product, and check the four obvious collision zones by hand through a full circuit before applying power. Pay particular attention to the return path, which is where unmodelled interference usually turns up.

Cycle validation

Run at target takt — actual product weight, actual speed, actual duty cycle — and measure: attachment hole elongation, plate deflection under load, pin rotation against a witness mark, drive current or torque drift, and chain elongation growth after a defined number of cycles. Re-torque after the first block of running hours. Only then freeze the revision.

Cost Control: Standard Versus Custom

The most effective cost strategy is to keep the chain body standard and customise only the attachment. You then buy the base material from stock anywhere in the world and treat the special plate as a scheduled, engineered purchase rather than a machine-critical single-source item.

What drives the price

Tooling: simple plates can be laser cut for prototypes in small batches; volume normally justifies a blanking die or progressive tool whose cost has to be amortised across the run.
Minimum order quantity: tooling economics set a practical threshold, typically tens of pieces for laser-cut prototypes and considerably more once a die is involved.
Batch frequency: set-up and handling dominate small batches, so consolidating quantity into fewer, larger orders reduces unit cost substantially.
Lead time: standard attachment chain ships from stock; customs add drawing approval, tooling, first article inspection and then production.
Secondary operations: heat treatment specification, plating type, machining and packing each add both cost and calendar days.

Set against purchase price, weigh the downtime cost of the wrong decision. Field failures from attachment loosening or plate cracking cost vastly more than the tooling they were avoided to save, particularly where custom parts cannot be sourced locally on short notice.

Incoming and Outgoing Inspection, and How Attachments Fail

Goods-in checks worth doing

Length accuracy over a stated number of pitches, measured under standard measuring load.
Attachment hole position verified with a pin gauge and fixture rather than a rule.
Retention strength on sample pieces — push-out force of the plate-to-plate joint.
Pin rotation check with a witness mark and a torque attempt on a restrained sample.
Hardness and case depth on samples, plus plating thickness and bake verification where applicable.
Free articulation through the wrap with no binding and no attachment-to-link contact.

Outgoing and packing

Verify attachment count and spacing against the order, confirm that plates are flat and undamaged, protect projected plates in packing so they cannot be bent in transit, apply the specified pre-lubrication, and keep stainless and carbon steel separated so there is no cross-contamination before installation.

The three common failures

Attachment loosening: usually the pin or plate rotating in its joint. Causes include insufficient interference, over-torque during installation, single-hole plates with no anti-rotation feature, and bending moments exceeding what the joint can resist.
Pin rotation: the classic failure of extended pin assemblies. Once the pin turns relative to the outer plate, the hole enlarges, pitch lengthens locally, and the chain begins to index late; in hollow pin designs the same mechanism destroys bore geometry.
Plate cracking: initiates at hole edges, at the neck fillet, or inside the bend radius of a bent plate. Typical causes are excessive bending arm, insufficient bend radius for the thickness, unaccounted cyclic loading, poor grain direction control, or hydrogen embrittlement from plating without baking.

The corresponding fixes are predictable: shorten the lever arm, support large plates with a second hole or a wing configuration, increase plate thickness or material grade, cancel the moment by loading symmetrically, add an idler or support rail closer to the load point, and specify plating with the correct bake cycle.

Post time: Oct-19-2026

Attachment and Specialty Roller Chains: Hollow Pin, Extended Pin and Custom Attachments for Conveyor Builders