There are actually two types of links alternating in the bush roller chain. The initial type is internal links, having two internal plates held collectively by two sleeves or bushings upon which rotate two rollers. Internal links alternate with the second type, the outer links, consisting of two outer plates held with each other by pins passing through the bushings of the internal links. The “bushingless” roller chain is similar in operation though not in construction; instead of separate bushings or sleeves holding the inner plates together, the plate has a tube Drive Chain stamped involved with 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 in comparison to simpler designs, resulting in higher efficiency and less wear. The initial power transmission chain types lacked rollers and bushings, with both the inner and external plates held by pins which straight contacted the sprocket the teeth; however this configuration exhibited extremely rapid wear of both the sprocket tooth, and the plates where they pivoted on the pins. This problem was partially solved by the advancement of bushed chains, with the pins holding the outer plates moving through bushings or sleeves linking the internal plates. This distributed the use over a larger area; however the teeth of the sprockets still wore quicker than is appealing, from the sliding 
friction against the bushings. The addition of rollers around the bushing sleeves of the chain and provided rolling contact with one’s teeth of the sprockets leading to excellent resistance to use of both sprockets and chain as well. There is even suprisingly low friction, provided that the chain is certainly sufficiently lubricated. Constant, clean, lubrication of roller chains is usually of main importance for efficient operation and also correct tensioning.