A spoke wrench or spoke key is a small wrench or tool used to adjust the tension in the spokes of a bicycle wheel by tightening or loosening individual spokes. A spoke wrench is sometimes more accurately called a nipple wrench (not to be confused with a nipple wrench in plumbing), as it is the spoke nipple and not the spoke itself that is turned.

Each spoke is threaded into a nipple which is fixed in a socket in the wheel's rim. The end of the nipple is square shaped.

Care must be taken when changing spoke tension because it is very easy to turn the nipple in the wrong direction and put the wheel out of true; that is, the wheel will spin crooked.

Common sizes include:

• .127" (3.23 mm)
• .130" (3.30 mm)
• .136" (3.45 mm)

In Plumbing

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In plumbing, a nipple wrench is often known as an inside pipe wrench, since it is the converse of a regular (outside) pipe wrench. An eccentric toothed gear is mounted on a hexagonal shaft. The wrench is introduced inside the pipe (especially a plumbing nipple, which has threading its entire length, and therefore no surface for an outside wrench); as the wrench is turned, the eccentric gear is forced to grip the inside of the pipe. As with a regular pipe wrench, the mechanism is such that the grip on the pipe increases with the torque applied on the wrench. They are a relatively obscure but often indispensable tool.

Bicycle tools | Plumbing | Nippelspanner