There are actually two types of links alternating in the bush Conveyor Chain roller chain. The 1st type is internal links, having two inner plates held collectively by two sleeves or bushings upon which rotate two rollers. Internal links alternate with the next type, the outer links, comprising two external plates held jointly by pins passing through the bushings of the inner links. The “bushingless” roller chain is comparable in operation though not in building; instead of individual bushings or sleeves holding the inner plates collectively, the plate has a tube stamped into it protruding from the hole which serves the same purpose. This has the advantage of removing one part of assembly of the chain.
The roller chain design reduces friction compared 
to simpler designs, leading to higher efficiency and less wear. The original power transmission chain types lacked rollers and bushings, with both the inner and outer plates kept by pins which straight contacted the sprocket the teeth; however this configuration exhibited extremely rapid wear of both the sprocket teeth, and the plates where they pivoted on the pins. This issue was partially solved by the advancement of bushed chains, with the pins keeping the outer plates moving through bushings or sleeves connecting the internal plates. This distributed the wear over a greater area; however the teeth of the sprockets still wore more rapidly than is appealing, from the sliding friction against the bushings. The addition of rollers surrounding the bushing sleeves of the chain and supplied rolling contact with the teeth of the sprockets resulting in excellent resistance to wear of both sprockets and chain aswell. There is even very low friction, as long as the chain is definitely sufficiently lubricated. Constant, clean, lubrication of roller chains is usually of main importance for efficient operation in addition to correct tensioning.