What is "curb pins"

Curb \Curb\, n.

1. That which curbs, restrains, or subdues; a check or hindrance; esp., a chain or strap attached to the upper part of the branches of a bit, and capable of being drawn tightly against the lower jaw of the horse.

   He that before ran in the pastures wild Felt the stiff curb control his angry jaws.
   --Drayton.

   By these men, religion,that should be The curb, is made the spur of tyranny.
   --Denham.

2. (Arch.) An assemblage of three or more pieces of timber, or a metal member, forming a frame around an opening, and serving to maintain the integrity of that opening; also, a ring of stone serving a similar purpose, as at the eye of a dome.

3. A frame or wall round the mouth of a well; also, a frame within a well to prevent the earth caving in.

4. A curbstone.

5. (Far.) A swelling on the back part of the hind leg of a horse, just behind the lowest part of the hock joint, generally causing lameness.
   --James Law.

   Curb bit, a stiff bit having branches by which a leverage is obtained upon the jaws of horse.
   --Knight.

   Curb pins (Horology), the pins on the regulator which restrain the hairspring.

   Curb plate (Arch.), a plate serving the purpose of a curb.

   Deck curb. See under Deck.