There are actually two types of links alternating in the bush roller chain. The first type is internal links, having two internal plates held jointly by two sleeves or bushings upon which rotate two rollers. Internal links alternate with the next type, the outer links, consisting of two outer plates held jointly by pins passing through the bushings of the internal links. The “bushingless” roller chain is comparable in operation though not in structure; 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 benefit of removing one step in assembly of the chain.
The roller chain design reduces friction in comparison to simpler designs, leading to higher efficiency and less wear. The original power transmission chain varieties lacked rollers and bushings, with both inner and outer plates kept by pins which directly contacted the sprocket tooth; nevertheless this configuration exhibited extremely rapid use 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 passing through bushings or sleeves connecting the inner 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 encircling the bushing sleeves of the chain and offered rolling contact with the teeth of the sprockets leading to excellent resistance to put on of both sprockets and chain aswell. There is even very low friction, as long as the chain can be sufficiently lubricated. Constant, clean, lubrication of roller chains can be of main importance for efficient operation as well as correct tensioning.