There are two types of links alternating in the bush roller chain. The 1st type is inner links, having two inner plates held together by two sleeves or bushings upon which rotate two rollers. Inner links Drive Chain alternate with the next type, the external links, comprising two outer plates held together by pins moving through the bushings of the inner links. The “bushingless” roller chain is similar in operation though not in structure; instead of separate bushings or sleeves holding the inner plates collectively, the plate has a tube stamped into it protruding from the hole which serves the same purpose. This has the advantage of removing one step in assembly of the chain.
The roller chain design reduces friction compared to simpler designs, resulting in higher efficiency and less wear. The initial power transmission chain varieties lacked rollers and bushings, with both the inner and external plates kept by pins which directly contacted the sprocket tooth; nevertheless this configuration exhibited extremely rapid use of both the sprocket the teeth, and the plates where they pivoted on the pins. This issue was partially solved by the development of bushed chains, with the pins holding the outer plates passing through bushings or sleeves connecting the inner plates. This distributed the wear over a larger area; however the teeth of the sprockets still wore quicker 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 use of both sprockets and chain aswell. There is even suprisingly low friction, as long as the chain is certainly sufficiently lubricated. Constant, clean, lubrication 
of roller chains is certainly of primary importance for efficient procedure in addition to correct tensioning