A rubber expanding drum is an accessory piece used for grinding with a spiral wound band. If contains a tightening nut which has a reverse thread. Once a band is placed on the drum and the nut is tightened, the diameter of the rubber drum expands, allowing it to firmly hold the band in place. Because of the reverse thread, it self-tightens the band while running. Click for Product Info on Spiral Wound Bands. Rubber Expanding Drums An expanding rubber drum is specified by three measurements. They are: 1) the diameter, which corresponds to the diameter of the band. 2) the width, corresponding to the width of the band. 3) the shank diameter, which is generally 1/8" for small diameters, 1/4" for most, and up to 3/8" in the largest diameter drums. Below are listed the drums we keep in stock. Dia: 1/4" Width 1/2" Shank Dia: 1/8" Max RPMs: 30,000 Dia: 1/4" Width 3/4" Shank Dia: 1/8" Max RPMs: 30,000 Dia: 1/4" Width 1" Shank Dia: 1/8" Max RPMs: 25,000 Dia: 3/8" Width 1/2" Shank Dia: 1/8" Max RPMs: 30,000 Dia: 3/8" Width 3/4" Shank Dia: 1/8" Max RPMs: 30,000 Dia: 3/8" Width 1" Shank Dia: 1/8" Max RPMs: 25,000 Dia: 1/2" Width 1/2" Shank Dia: 1/8" Max RPMs: 30,000 Dia: 1/2" Width 1/2" Shank Dia: 1/4" Max RPMs: 30,000 Dia: 1/2" Width 3/4" Shank Dia: 1/8" Max RPMs: 25,000 Dia: 1/2" Width 3/4" Shank Dia: 1/4" Max RPMs: 30,000 Dia: 1/2" Width 1" Shank Dia: 1/8" Max RPMs: 25,000 Dia: 1/2" Width 1" Shank Dia: 1/4" Max RPMs: 20,000 Dia: 1/2" Width 1-1/2" Shank Dia: 1/4" Max RPMs: 20,000 Dia: 3/4" Width 1/2" Shank Dia: 1/8" Max RPMs: 20,000 Dia: 3/4" Width 1/2" Shank Dia: 1/4" Max RPMs: 25,000 Dia: 3/4" Width 3/4" Shank Dia: 1/8" Max RPMs: 18,000 Dia: 3/4" Width 3/4" Shank Dia: 1/4" Max RPMs: 24,000 Dia: 3/4" Width 1" Shank Dia: 1/4" Max RPMs: 22,000 Dia: 3/4" Width 1-1/2" Shank Dia: 1/4" Max RPMs: 18,000 Dia: 3/4" Width 2" Shank Dia: 1/4" Max RPMs: 15,000 Dia: 1" Width 1" Shank Dia: 1/4" Max RPMs: 19,000 Dia: 1" Width 1-1/2" Shank Dia: 1/4" Max RPMs: 15,000 Dia: 1" Width 2" Shank Dia: 1/4" Max RPMs: 12,000 Dia: 1" Width 3" Shank Dia: 1/4" Max RPMs: 8,000 Dia: 1-1/4" Width 1" Shank Dia: 1/4" Max RPMs: 15,000 Dia: 1-1/4" Width 1-1/2" Shank Dia: 1/4" Max RPMs: 12,000 Dia: 1-1/4" Width 2" Shank Dia: 1/4" Max RPMs: 10,000 Dia: 1-1/2" Width 3/4" Shank Dia: 1/4" Max RPMs: 15,000 Dia: 1-1/2" Width 1" Shank Dia: 1/4" Max RPMs: 14,000 Dia: 1-1/2" Width 1-1/2" Shank Dia: 1/4" Max RPMs: 12,000 Dia: 1-1/2 Width 2" Shank Dia: 1/4" Max RPMs: 9,000 Dia: 2" Width 1" Shank Dia: 1/4" Max RPMs: 10,000 Dia: 2" Width 1-1/2" Shank Dia: 1/4" Max RPMs: 9,000 Dia: 2" Width 2" Shank Dia: 1/4" Max RPMs: 7,000 Dia: 2" Width 3" Shank Dia: 1/4" Max RPMs: 5,000 Dia: 3" Width 1" Shank Dia: 3/8" Max RPMs: 7,000 Dia: 3" Width 1-1/2" Shank Dia: 3/8" Max RPMs: 6,000 Dia: 3" Width 2" Shank Dia: 3/8" Max RPMs: 4,000 Dia: 3" Width 3" Shank Dia: 3/8" Max RPMs: 3,600