What is "knuckle joint"

Knuckle \Knuc"kle\, n. [OE. knokel, knokil, AS. cuncel; akin to D. knokkel, OFries. knokele, knokle, G. kn["o]chel, Sw. knoge, Dan. knokkel, G. knochen bone, and perh. to E. knock.]

1. The joint of a finger, particularly when made prominent by the closing of the fingers.
   --Davenant.

2. The kneejoint, or middle joint, of either leg of a quadruped, especially of a calf; -- formerly used of the kneejoint of a human being.

   With weary knuckles on thy brim she kneeled sadly down.
   --Golding.

3. The joint of a plant. [Obs.]
   --Bacon.

4. (Mech.) The joining parts of a hinge through which the pin or rivet passes; a knuckle joint.

5. (Shipbuilding) A convex portion of a vessel's figure where a sudden change of shape occurs, as in a canal boat, where a nearly vertical side joins a nearly flat bottom.

6. A contrivance, usually of brass or iron, and furnished with points, worn to protect the hand, to add force to a blow, and to disfigure the person struck; -- called also knuckle duster, knuckles or brass knuckles. [Slang.]

   Knuckle joint (Mach.), a hinge joint, in which a projection with an eye, on one piece, enters a jaw between two corresponding projections with eyes, on another piece, and is retained by a pin which passes through the eyes and forms the pivot.

   Knuckle of veal (Cookery), the lower part of a leg of veal, from the line of the body to the knuckle.

1. n. a joint of a finger when the fist is closed [syn: knuckle, metacarpophalangeal joint]

2. a joint allowing movement in one plane only [syn: hinge joint]

A knuckle joint is a mechanical joint used to connect two rods which are under a tensile load, when there is a requirement of small amount of flexibility, or angular moment is necessary. There is always axial or linear line of action of load.