The ATB, Copper, Dome Base features straps constructed from 1-inch wide soft temper copper which smoothly forms to fit every type of conical shape. This copper dome air terminal base has a 5/8-inch externally threaded hub diameter and four 4-inch straps with two 3/16-inch mounting holes per strap. It can accept all Class I and Class II conductors. All threads are UNC. For mounting this base, you will need air terminal adapters. ISP Supplies is a certified distributor of Harger, offering its certified Copper Air Terminal Bases at the best value.