In almost every respect except the basic idea - it is built for load and abuse rather than for speed and precision.

A precision roller chain has a small pitch, close tolerances, hardened components and a finish suited to running fast in a lubricated enclosure. It transmits power between two shafts.

An engineering chain has a large pitch, heavy sidebars, big pins with generous bearing area, and construction that may be cast, forged or fabricated. It runs slowly, carries very high loads, and typically works in dust, grit, water or process material rather than in oil.

Crucially, it usually carries the material as well: attachments bolted to or formed in the links hold buckets, flights or slats, so the chain is the conveyor rather than the drive to it.

The selection process differs accordingly - working load, environment and attachment arrangement rather than transmitted power at speed.

Extended pins, bent and straight lugs, integral flights, bucket mountings and bolt-on brackets - and the attachment spacing is part of the chain specification.

Attachments convert the chain into a conveying element. Bucket elevator chains carry mountings at regular intervals for the buckets. Drag conveyor chains carry flights that push material along a trough. Apron feeders carry slats or pans bolted to lugs on the links.

The attachments may be formed as part of the link sidebar, welded on, or bolted to a plain link, and each approach trades strength against replaceability.

Spacing is stated as an attachment on every link, every second link, every third and so on, and it must match the buckets or flights being carried.

When ordering replacement chain, the attachment type and spacing matter as much as the pitch and strength - a correct chain with the wrong attachment pitch is unusable.

On working load with a generous factor over breaking load, then on the environment - not on transmitted power.

Manufacturers publish both an ultimate breaking load and a maximum allowable working load, and the ratio between them is large because these chains operate with shock, uneven loading and progressive wear.

The working load must account for the material being carried, the friction of dragging it, the lift on an inclined or vertical run, and the starting condition - a bucket elevator started full presents far more load than one started empty.

Then the environment governs material and finish: abrasion resistance for aggregates and cement, corrosion resistance for water treatment and food processing, temperature capability for kilns and dryers.

Speed rarely constrains, because these chains run slowly. Where they do run faster, check the manufacturer's limit, since large-pitch chain suffers pronounced chordal action that produces vibration and dynamic loading at speed.

Because they let a chain be made to any length and repaired without needing a separate connecting link.

A straight sidebar chain alternates wide and narrow links, so it can only be made in an even number of pitches and needs a special connecting link to close the loop - which is usually the weakest point.

An offset link has one wide end and one narrow end, so every link connects to the next identically. Any number of links can be assembled, the chain can be made to an exact length, and a damaged link can be removed and replaced with a standard one on site.

That matters enormously on conveyor and elevator chain, where the chain is long, cut to fit the machine, and repaired in place during shutdowns rather than being replaced as a complete loop.

The trade is a slightly lower strength for a given size and a chain that is directional - it must be installed the right way round relative to the direction of pull.

Abrasive wear at the pin and bush, corrosion, and shock loading - with wear usually presenting as elongation.

Abrasive material working into the pin joints is the dominant wear mechanism. Unlike a transmission chain running in clean oil, an engineering chain is often immersed in exactly the abrasive material it is conveying, and the joint is the one place that must articulate.

That wear shows as elongation. As the chain lengthens it no longer matches the sprocket pitch, so it rides higher on the teeth, loads them unevenly, and eventually jumps. Sprocket wear accelerates in parallel.

Corrosion attacks the joint from the other direction in wet, chemical and food-processing environments, and can seize joints so links stop articulating - which then fails the sidebars in bending.

Shock from starting a loaded machine, from material surges and from jams delivers loads far above running load. Measure elongation on a schedule and replace sprockets with chain, since worn sprockets destroy new chain quickly.

Usually yes - fitting new chain to worn sprockets wastes the chain, and the saving is false.

As a chain elongates, it seats progressively further out on the sprocket teeth and wears them into a hooked profile that matches the elongated pitch. Those worn teeth then no longer match a new chain at its correct pitch.

A new chain on hooked sprockets is loaded on very few teeth, engages badly, wears rapidly, and can climb and jump. The new chain's life may be a fraction of what it should be.

So the normal practice is to replace chain and sprockets as a set. Where budget forces a choice, inspect the sprocket tooth profile against a new-tooth template - a lightly worn sprocket may be acceptable.

On long conveyors it is also worth checking whether the chain has worn unevenly along its length, since replacing only a damaged section leaves new links running with elongated ones, which loads them unevenly.

Carbon and alloy steels with a range of heat treatments, plus stainless and specialist coatings for corrosive and hygienic duty.

Standard carbon steel with through-hardened or case-hardened pins and bushes covers general conveying. Alloy steels are used where strength must rise without increasing size.

Abrasion-resistant variants harden the wearing surfaces more aggressively or use induction-hardened pins and bushes, which extends life substantially in aggregate, cement and mining duty.

Stainless chain is used in water and wastewater treatment, food and beverage processing, and chemical plant, where corrosion would otherwise seize the joints. It has lower strength than carbon steel for the same size, so the chain must be sized accordingly.

Coatings - galvanising, specialist platings and polymer finishes - offer a middle route where full stainless is not justified.

State the material being conveyed, its moisture and chemistry, and the temperature, since these decide the specification more than the load does.