There are actually two types of links alternating in the bush roller chain. The first type is internal links, having two inner plates held together by two sleeves or bushings where rotate two rollers. Inner links alternate with the second type, the outer links, consisting of 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 separate bushings or sleeves keeping the inner plates together, the plate has a tube stamped into it protruding from the hole which serves the same purpose. It has the benefit 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 original power transmission chain types lacked rollers and bushings, with both inner and external plates kept by pins which directly contacted the sprocket teeth; nevertheless this configuration exhibited incredibly rapid use of both the sprocket the teeth, 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 passing through bushings or sleeves linking the internal plates. This distributed the use over a greater 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 provided rolling contact with one’s teeth of the sprockets resulting in excellent resistance to put on of both sprockets and chain as well. There is even suprisingly low friction, as long as the chain is usually sufficiently lubricated. Continuous, clean, lubrication of roller chains is of major importance for efficient operation in addition to correct Drive Chain tensioning.
