There are 
two types of links alternating in the bush roller chain. The initial type is internal links, having two inner plates held jointly by two sleeves or Transmission Chain bushings upon which rotate two rollers. Inner links alternate with the next type, the outer links, comprising two external plates held collectively by pins passing through the bushings of the internal links. The “bushingless” roller chain is comparable in procedure though not in construction; instead of separate bushings or sleeves holding the inner plates jointly, the plate has a tube stamped into 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 original power transmission chain varieties lacked rollers and bushings, with both inner and external plates held by pins which directly contacted the sprocket the teeth; however this configuration exhibited extremely rapid put on of both the sprocket the teeth, and the plates where they pivoted on the pins. This problem was partially solved by the development 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 larger area; however the the teeth 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 provided rolling contact with the teeth of the sprockets resulting in excellent resistance to use of both sprockets and chain aswell. There is even very low friction, provided that the chain is sufficiently lubricated. Continuous, clean, lubrication of roller chains is certainly of primary importance for efficient operation and also correct tensioning.