The addition of a keyway allows for use in positive drive applications as a shaft collar or for extra torque capacity when used as a rigid coupling.125", Stainless, OD 1 7/8" Ruland clamp style shaft collars do not mar the shaft, are infinitely adjustable, and have superior holding power when compared to set screw collars.125" bore, 1/4" keyway, 1 7/8" OD, and 1 1/16" width..