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SESK: Stuff Everyone Should Know · sesk.info/bike-valve-presta-locknut

Which bike valve is thinner and has a small locknut you unthread before adding air?

A Presta valve.

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  1. Schrader
  2. Woods (Dunlop)
  3. Presta ✔

Why: Presta stems are about 6 mm wide, thinner than Schrader. The small locknut on top must be unthreaded before air can go in.

Huh, didn't know that: Presta is the 'French' valve and Schrader the 'American' valve.

The dad joke
Why did the Presta valve feel proud? It was at the top of its class.
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References

Answer: Presta. Presta stems are about 6 mm wide, thinner than Schrader. The small locknut on top must be unthreaded before air can go in.

  1. Park Tool: Tire and Tube Removal and Installation www.parktool.com/en-us/blog/repair-help/tire-and-tube-removal-and-installation
    Presta stems are nominally 6mm (1/4″) diameter, thinner than Schrader valves. At the top of the stem is a small locknut
    Checked 2026-10-12.

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