Coag n. See Coak, a kind of tenon.
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  Coak, n.
  1. Carp. A kind of tenon connecting the face of a scarfed timber with the face of another timber, or a dowel or pin of hard wood or iron uniting timbers. [Also spelt coag.]
  2. A metallic bushing or strengthening piece in the center of a wooden block sheave.