The handles are drop-forged from one piece of steel with extra long fine thread bolts for secure semi-permanent assembly.
Each handle is of a length to fit an exact number of standard weight plates. The #1 handle holds 1 plate per side, the #2 handle holds 2 plates per side, and so on. They are tightened with the included bolts and are meant to be semi-permanently assembled, usually as part of a large set.
Refer to the list below for what size of dumbbell you can assemble with each size handle. Each handle plus end caps are rounded off to weigh about 5 lbs together, so a 30lb dumbbell would have 25lbs of weight plates.