There are actually two types of links alternating in the bush roller chain. The 1st type is inner links, having two inner plates held with each other by two sleeves or bushings where rotate two rollers. Inner links alternate with the second type, the outer links, comprising two outer plates held collectively by pins moving through the bushings of the inner links. The "bushingless" roller chain is comparable in operation though not in structure; instead of separate bushings or sleeves keeping the inner plates with each other, 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 initial power transmission chain types lacked rollers and bushings, with both the inner and outer plates held by pins which straight contacted the sprocket the teeth; nevertheless this configuration exhibited extremely rapid wear of both sprocket the teeth, and the plates where they pivoted on the pins. This Conveyor Chain problem was partially solved by the advancement of bushed chains, with the pins holding the outer plates moving through bushings or sleeves linking the inner plates. This distributed the put on over a larger area; however the tooth 
of the sprockets still wore quicker than is desired, from the sliding friction against the bushings. The addition of rollers surrounding the bushing sleeves of the chain and provided rolling contact with one's teeth of the sprockets resulting in excellent resistance to wear of both sprockets and chain as well. There is even suprisingly low friction, so long as the chain is usually sufficiently lubricated. Constant, clean, lubrication of roller chains is of primary importance for efficient procedure and also correct tensioning.