Spoke wrench, purchased to fit nipples on spokes. A spoke wrench (or spoke key) is used to tighten or slacken spoke tensions whilst building or truing a rim.

Park Tool spoke wrenches come in these 5 sizes: SW-0, SW-1, SW-2, SW-3, or SW-7

1. The SW-0: is sized for 3.22mm (0.127") nipples and fits Wheelsmith, Marwi and DT, Edco as well as other brands of nipples.
2. The SW-1: 3.3mm /80 ga./.130 nipple
3. The SW-2: 3.45mm /80 ga./.136 nipple
4. The SW-3: 3.96mm /105 ga./.156 nipple

A typical spoke key:

• produced by respected company 'Park Tool usa'