There are actually two types of links alternating in the bush roller chain. The first type is inner 
links, having two inner plates held agricultural Chain jointly by two sleeves or bushings upon which rotate two rollers. Internal links alternate with the next type, the external links, consisting of two outer plates held with each other by pins passing through the bushings of the internal links. The “bushingless” roller chain is comparable in procedure though not in building; 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 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 varieties lacked rollers and bushings, with both inner and external plates held by pins which straight contacted the sprocket teeth; nevertheless this configuration exhibited extremely rapid put on of both the sprocket 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 moving through bushings or sleeves connecting the internal plates. This distributed the put on over a larger area; however the the teeth of the sprockets still wore more rapidly than is desired, from the sliding friction against the bushings. The addition of rollers around the bushing sleeves of the chain and offered 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 can be sufficiently lubricated. Constant, clean, lubrication of roller chains is certainly of principal importance for efficient operation along with correct tensioning.