The 10rd drum has a diameter of 6.75".Will only fit 1927-a1 thompson models and modern thompson guns made in worcester, ma.*note will not fit thompson m1 models (military version of thompson-if it has a side charging handle then it is an thompson m1 model) and thompson guns made in west hurley, ny or before 1990.Each drum is shipped with a drum installation device (3rd hand.Each authentic drum is entirely u.S.Manufactured to the exact specifications as the originals.Caliber: 45 ACPCapacity: 10rdFinish: BlackModel: A1Material: SteelType: DrumModel Fit: Tommy GunBrand Fit: ThompsonCapacity: 10