A metric taper bushed sprocket is a sprocket where a tapered bushing is bolted into the taper bore that is machined in the sprocket. When installed this bushing is compressed onto the shaft providing a tight grip. Taper bushed sprockets have a tapered bushing bolted into a taper bore with hex head set screws instead of bolts. Martin Roller Chain Sprocket, Type B Double Strand Solid Stock Bore, 50.8 mm Bore, 121.45 mm OD, #12B-2 Chain, 18 Teeth, 19.05 mm Pitch, 109.7 mm Pitch Diameter, 90 mm Diameter Hub, 31.75 mm Length Through Bore, 2012 Taper Bushing, High Carbon Steel