pinwrench

/ˈpɪnˌrɛntʃ/
noun
  1. A tool with a pin or pins that fits into holes or slots in a fastener, used to tighten or loosen it.
    • The pinwrench has two pins that fit into the holes of the nut for a secure grip.
    • The mechanic used a pinwrench to adjust the bicycle's bottom bracket.
    • You'll need a pinwrench to remove the lock ring on that gear.
Synonyms
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