B series precision roller chain or British standard roller chain is made in accordance with ISO 606 B, BS 228, and DIN 8187 European standards. These chains resemble standard ANSI roller chains (A series precision roller chains). However, they are dimensionally different and can not operate on ANSI sprockets. 

A roller chain is a series of roller links and pin links alternately assembled, and joined throughout the length of the chain. Each roller link consists of two rollers, slipped into bushings, then press-fitted into inner side plates. The pin links are made up of two pins press-fitted into two outer plates. 

Roller chain sizes are determined by four primary dimensions: pitch, inside width of the roller link, roller diameter, and plate thickness. Pitch, the distance between centers of adjacent flexing joints, forms the proportional basis for the remaining dimensions.