Forelock /(?)/

Fore·lock

Forelock

n.
  1. The lock of hair that grows from the forepart of the head.
  2. A cotter or split pin, as in a slot in a bolt, to prevent retraction; a linchpin; a pin fastening the cap-square of a gun. (Mech.)
    Time is painted with a lock before and bald behind, signifying thereby that we must take time by the forelock; for when it is once past, there is no recalling it.
    On occasion's forelock watchful wait.

Phrases & Compounds
Forelock bolt
a bolt retained by a key, gib, or cotter passing through a slot.
Forelock hook
a winch or whirl by which a bunch of three yarns is twisted into a standard.
To take time by the forelock
to make prompt use of anything; not to let slip an opportunity.