Bar ends are 5/8" diameter to fit 5/8-inch holes. With a Torquewinder tool, winding garage door torsion springs is safer and easier than using basic winding bars or rods. Safer, Easier, and No more dropped bars. Safer because a spring assists each bar to fully insert more quickly and stay engaged whenever both bars are inserted. The spring assists faster insertion as you rotate through the pockets of a spring cone. You won't drop a bar when changing hands because they’re connected. The Torquewinder won’t roll off a flat surface like single bars do. Conveniently carry your Torquewinder in a tool belt or hammer loop. A rugged sleeve covers the durable inner spring. Bars are made of High Yield Strength steel.