There are actually two types of links alternating in the bush roller chain. The first type is inner links, having two internal plates held together by two sleeves or bushings where rotate two rollers. Internal links alternate with the second type, the outer links, consisting of two outer plates held together by pins Conveyor Chain passing through the bushings of the internal links. The “bushingless” roller chain is similar in operation though not in structure; instead of individual bushings or sleeves keeping the inner plates collectively, the plate includes a tube stamped into it protruding from the hole which serves the same purpose. It has the advantage of removing one part of assembly of the chain.
The roller chain design reduces friction compared to simpler designs, resulting in higher efficiency and less wear. The original power transmission chain varieties lacked rollers and bushings, with both the inner and outer plates held by pins which straight contacted the sprocket tooth; nevertheless this configuration exhibited incredibly rapid use of both sprocket teeth, and the plates where they pivoted on the pins. This problem was partially solved by the advancement of bushed chains, with the pins keeping the outer plates moving through bushings or sleeves connecting the inner plates. This distributed the put on over a larger area; however the tooth of the sprockets still wore quicker than is desirable, from the sliding friction against the 
bushings. The addition of rollers surrounding 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 suprisingly low friction, as long as the chain is sufficiently lubricated. Continuous, clean, lubrication of roller chains is certainly of main importance for efficient operation and also correct tensioning.