There are actually two types of links alternating in the bush roller chain. The first type is internal links, having two internal plates held together by two sleeves or Transmission Chain bushings where rotate two rollers. Inner links alternate with the next type, the outer links, comprising two outer plates held collectively by pins moving through the bushings of the internal links. The “bushingless” roller chain is comparable in procedure though not in construction; instead of individual 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, resulting in higher efficiency and less wear. The initial power transmission chain types lacked rollers and bushings, with both the inner and outer plates kept by pins which straight contacted the sprocket teeth; however this configuration exhibited extremely rapid use of both 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 linking the inner plates. This distributed the put on over a larger area; however the the teeth of the sprockets still wore quicker than is attractive, 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 wear 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.