What is "pin hole"

Pin \Pin\, n. [OE. pinne, AS. pinn a pin, peg; cf. D. pin, G. pinne, Icel. pinni, W. pin, Gael. & Ir. pinne; all fr. L. pinna a pinnacle, pin, feather, perhaps orig. a different word from pinna feather. Cf. Fin of a fish, Pen a feather.]

1. A piece of wood, metal, etc., generally cylindrical, used for fastening separate articles together, or as a support by which one article may be suspended from another; a peg; a bolt.

   With pins of adamant And chains they made all fast.
   --Milton.

2. Especially, a small, pointed and headed piece of brass or other wire (commonly tinned), largely used for fastening clothes, attaching papers, etc.

3. Hence, a thing of small value; a trifle.

   He . . . did not care a pin for her.
   --Spectator.

4. That which resembles a pin in its form or use; as:

   1. A peg in musical instruments, for increasing or relaxing the tension of the strings.

   2. A linchpin.

   3. A rolling-pin.

   4. A clothespin.

   5. (Mach.) A short shaft, sometimes forming a bolt, a part of which serves as a journal. See Illust. of Knuckle joint, under Knuckle.

   6. (Joinery) The tenon of a dovetail joint.

5. One of a row of pegs in the side of an ancient drinking cup to mark how much each man should drink.

6. The bull's eye, or center, of a target; hence, the center. [Obs.] ``The very pin of his heart cleft.''
   --Shak.

7. Mood; humor. [Obs.] ``In merry pin.''
   --Cowper.

8. (Med.) Caligo. See Caligo.
   --Shak.

9. An ornament, as a brooch or badge, fastened to the clothing by a pin; as, a Masonic pin.

10. The leg; as, to knock one off his pins. [Slang] Banking pin (Horol.), a pin against which a lever strikes, to limit its motion. Pin drill (Mech.), a drill with a central pin or projection to enter a hole, for enlarging the hole, or for sinking a recess for the head of a bolt, etc.; a counterbore. Pin grass. (Bot.) See Alfilaria. Pin hole, a small hole made by a pin; hence, any very small aperture or perforation. Pin lock, a lock having a cylindrical bolt; a lock in which pins, arranged by the key, are used instead of tumblers. Pin money, an allowance of money, as that made by a husband to his wife, for private and personal expenditure. Pin rail (Naut.), a rail, usually within the bulwarks, to hold belaying pins. Sometimes applied to the fife rail. Called also pin rack. Pin wheel.

    1. A contrate wheel in which the cogs are cylindrical pins.

    2. (Fireworks) A small coil which revolves on a common pin and makes a wheel of yellow or colored fire.