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mast clamp

noun Nautical.
  1. a pierced slab of hardwood built into the deck structure of a small ship or boat to receive the force of the mast, which is fitted tightly through it.
  2. Also called mast hasp. a metal collar fitted to a thwart of a small boat to steady a mast.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018