Martin Sprocket & Gear 40BS21 Sprocket is a standard chain sprocket from Martin Sprocket & Gear, identified by the part number 40BS21. The available description notes “Martin 40BS21 3 4" Sprocket,” reflecting the catalog entry for this design. This sprocket functions as the driving element in chain-drive power transmission systems. Use the 40BS21 designation when sourcing exact matches for replacement or troubleshooting within this Martin product line.
