nab

At Clayton point and other nabs to the south of Scarborough.

The Toe, or Nab of the Bolt, which rises[…]above the Straight on the Top of the Bolt: The Office of this Nab, is to receive the Bottom of the Bit of the Key, when in turning it about, it shoots the Bolt backward or forwards.

the Bottom of the Bit may fall almost to the Bottom of the Nab , and shoot the Bolt back