There are actually two types of links alternating in the bush roller chain. The 1st type is inner links, having two internal plates held jointly by two sleeves or bushings where rotate two rollers. Internal links alternate with the second type, the outer links, consisting of two external plates held jointly by pins moving through the bushings of the internal links. 
The “bushingless” roller chain is comparable in operation though not in building; instead of individual bushings or sleeves holding the inner plates with each other, the plate has a tube stamped involved with it protruding from the hole which serves the same purpose. It has the benefit of removing one part of assembly of the chain.
The roller chain design reduces friction compared 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 straight contacted the sprocket the teeth; however this configuration exhibited incredibly rapid put on of both sprocket tooth, and the plates where they pivoted on the pins. This problem was partially solved by the advancement of bushed chains, with the pins holding the outer plates passing through bushings or sleeves linking the inner plates. This distributed the use over a agricultural Chain greater area; however the tooth of the sprockets still wore more rapidly than is appealing, from the sliding friction against the bushings. The addition of rollers around the bushing sleeves of the chain and supplied rolling contact with the teeth of the sprockets leading to excellent resistance to wear of both sprockets and chain aswell. There is even very low friction, as long as the chain is sufficiently lubricated. Continuous, clean, lubrication of roller chains can be of principal importance for efficient operation as well as correct tensioning