There are actually two types of links alternating in the bush roller chain. The first type is inner links, having two internal plates held with each other by two sleeves or bushings 
where rotate two rollers. Internal links alternate with the second type, the external links, consisting of two external plates held together by pins moving through the bushings of the inner links. The “bushingless” roller chain is similar in operation though not in building; instead of separate bushings or sleeves keeping the inner plates with each other, the plate includes a tube stamped involved with it protruding from the hole which serves the same purpose. It has the advantage of removing one step in 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 varieties lacked rollers and bushings, with both the inner and outer plates kept by pins which straight contacted the sprocket teeth; nevertheless this configuration exhibited extremely rapid use of both sprocket tooth, 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 Auto Chain connecting the inner plates. This distributed the put on over a larger area; however the teeth of the sprockets still wore more rapidly than is desired, from the sliding friction against the bushings. The addition of rollers encircling the bushing sleeves of the chain and offered rolling contact with the teeth of the sprockets leading to excellent resistance to wear of both sprockets and chain as well. There is even suprisingly low friction, so long as the chain is definitely sufficiently lubricated. Constant, clean, lubrication of roller chains is definitely of main importance for efficient procedure in addition to correct tensioning.