The ServoCity Set-Screw Shaft Coupler (4mm Round Bore to 6mm Round Bore) facilitates the connection of 4mm diameter shafts to 6mm diameter shafts. It features an M5 set-screw with a nylon locking patch to secure the shafts and prevent loosening. This coupler is ideal for applications with limited space and includes built-in shims to allow operation against a bearing without contacting the outer race.