20B-1 roller chain (British Standard / ISO 606 European B-series) features a pitch of 31.75 mm (1.25 inches), an inner roller width of 19.56 mm, and a roller diameter of 19.05 mm

Pitch (P): 31.75 mm (1 1/4″)Roller Width (Inner Width - W): 19.56 mmRoller Diameter (D): 19.05 mm (3/4″)Pin Diameter (d): 10.19 mmPlate Height (H): 26.40 mm