These handles, plates and end caps are for building your own semi-permanently assembled "pro style" dumbbells. The handles are sometimes referred to as SDH handles, from their model numbers SDH-1, SDH-2, etc.
Are you looking for adjustable dumbbell handles? See the Adjustable Dumbbells.
For pre-assembled dumbbells of this style, see our Troy Pro Style Dumbbells.
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.