There are actually two types of links alternating in the bush roller chain. The 1st type is inner links, having two inner plates held collectively by two Auto Chain sleeves or bushings upon which rotate two rollers. Inner links alternate with the next type, the outer links, comprising two outer plates held with each other by pins moving through the bushings of the inner links. The “bushingless” roller chain is comparable in operation though not in structure; instead of individual bushings or sleeves holding the inner plates collectively, the plate has 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 in comparison to simpler designs, resulting in higher efficiency and less wear. The initial power transmission chain varieties lacked rollers and bushings, with both inner and outer plates kept by pins which directly contacted the sprocket tooth; however this configuration exhibited extremely rapid wear of both the sprocket the 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 use over a greater area; however the tooth of the sprockets still wore more rapidly than is attractive, from the sliding friction against the bushings. The addition of rollers around the bushing sleeves of the chain and supplied 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 very low friction, provided that the chain can be sufficiently lubricated. Continuous, clean, lubrication of roller chains can be of principal importance for efficient operation as well as correct tensioning