Summit Collars, SCR-100-KW/1PK Solid Rigid Coupling 1"" ID, 2"" WIDE, 3"" LONG, BLACK OXIDE WITH KEYWAY, RC-100-KW RC-100-KW Solid Rigid Coupling 1″ ID with Keyway Black Oxide Finish Bore: 1″ Outer Diameter: 2″ Width: 3″ Screw: 3/8-16″ Weight: 32 oz each Keyway 1/4″ Set Screw Couplings are the most cost-effective Rigid Coupling, stock in black oxide however, we can quote stainless steel rigid couplings on request. Standard sizes 1/4″ to 2″ Inside Diameter (ID).