What is "spring pin"

Spring \Spring\, n. [AS. spring a fountain, a leap. See Spring, v. i.]

1. A leap; a bound; a jump.

   The prisoner, with a spring, from prison broke.
   --Dryden.

2. A flying back; the resilience of a body recovering its former state by its elasticity; as, the spring of a bow.

3. Elastic power or force.

   Heavens! what a spring was in his arm!
   --Dryden.

4. An elastic body of any kind, as steel, India rubber, tough wood, or compressed air, used for various mechanical purposes, as receiving and imparting power, diminishing concussion, regulating motion, measuring weight or other force.

   Note: The principal varieties of springs used in mechanisms are the spiral spring (Fig. a), the coil spring (Fig. b), the elliptic spring (Fig. c), the half-elliptic spring (Fig. d), the volute spring, the India-rubber spring, the atmospheric spring, etc.

5. Any source of supply; especially, the source from which a stream proceeds; an issue of water from the earth; a natural fountain. ``All my springs are in thee.''
   --Ps. lxxxvii. 7. ``A secret spring of spiritual joy.''
   --Bentley. ``The sacred spring whence right and honor streams.''
   --Sir J. Davies.

6. Any active power; that by which action, or motion, is produced or propagated; cause; origin; motive.

   Our author shuns by vulgar springs to move The hero's glory, or the virgin's love.
   --Pope.

7. That which springs, or is originated, from a source; as:

   1. A race; lineage. [Obs.]
      --Chapman.

   2. A youth; a springal. [Obs.]
      --Spenser.

   3. A shoot; a plant; a young tree; also, a grove of trees; woodland. [Obs.]
      --Spenser. Milton.

8. That which causes one to spring; specifically, a lively tune. [Obs.]
   --Beau. & Fl.

9. The season of the year when plants begin to vegetate and grow; the vernal season, usually comprehending the months of March, April, and May, in the middle latitudes north of the equator. ``The green lap of the new-come spring.''
   --Shak.

   Note: Spring of the astronomical year begins with the vernal equinox, about March 21st, and ends with the summer solstice, about June 21st.

10. The time of growth and progress; early portion; first stage; as, the spring of life. ``The spring of the day.''
    --1 Sam. ix. 26.

    O how this spring of love resembleth The uncertain glory of an April day.
    --Shak.

11. (Naut.)

    1. A crack or fissure in a mast or yard, running obliquely or transversely.

    2. A line led from a vessel's quarter to her cable so that by tightening or slacking it she can be made to lie in any desired position; a line led diagonally from the bow or stern of a vessel to some point upon the wharf to which she is moored. Air spring, Boiling spring, etc. See under Air, Boiling, etc. Spring back (Bookbinding), a back with a curved piece of thin sheet iron or of stiff pasteboard fastened to the inside, the effect of which is to make the leaves of a book thus bound (as a ledger or other account or blank book) spring up and lie flat. Spring balance, a contrivance for measuring weight or force by the elasticity of a spiral spring of steel. Spring beam, a beam that supports the side of a paddle box. See Paddle beam, under Paddle, n. Spring beauty.

       1. (Bot.) Any plant of the genus Claytonia, delicate herbs with somewhat fleshy leaves and pretty blossoms, appearing in springtime.

       2. (Zo["o]l.) A small, elegant American butterfly ( Erora l[ae]ta) which appears in spring. The hind wings of the male are brown, bordered with deep blue; those of the female are mostly blue.

          Spring bed, a mattress, under bed, or bed bottom, in which springs, as of metal, are employed to give the required elasticity.

          Spring beetle (Zo["o]l.), a snapping beetle; an elater.

          Spring box, the box or barrel in a watch, or other piece of mechanism, in which the spring is contained.

          Spring fly (Zo["o]l.), a caddice fly; -- so called because it appears in the spring.

          Spring grass (Bot.), vernal grass. See under Vernal.

          Spring gun, a firearm discharged by a spring, when this is trodden upon or is otherwise moved.

          Spring hook (Locomotive Engines), one of the hooks which fix the driving-wheel spring to the frame.

          Spring latch, a latch that fastens with a spring.

          Spring lock, a lock that fastens with a spring.

          Spring mattress, a spring bed.

          Spring of an arch (Arch.) See Springing line of an arch, under Springing.

          Spring of pork, the lower part of a fore quarter, which is divided from the neck, and has the leg and foot without the shoulder. [Obs.]
          --Nares.

          Sir, pray hand the spring of pork to me.
          --Gayton.

          Spring pin (Locomotive Engines), an iron rod fitted between the springs and the axle boxes, to sustain and regulate the pressure on the axles.

          Spring rye, a kind of rye sown in the spring; -- in distinction from winter rye, sown in autumn.

          Spring stay (Naut.), a preventer stay, to assist the regular one.
          --R. H. Dana, Jr.

          Spring tide, the tide which happens at, or soon after, the new and the full moon, and which rises higher than common tides. See Tide.

          Spring wagon, a wagon in which springs are interposed between the body and the axles to form elastic supports.

          Spring wheat, any kind of wheat sown in the spring; -- in distinction from winter wheat, which is sown in autumn.

A spring pin (also called tension pin or roll pin) is a mechanical fastener that secures the position of two or more parts of a machine relative to each other. Spring pins have a body diameter which is larger than the hole diameter, and a chamfer on either one or both ends to facilitate starting the pin into the hole. The spring action of the pin allows it to compress as it assumes the diameter of the hole. The radial force exerted by the pin against the hole wall retains it in the hole, therefore a spring pin is considered a self retaining fastener. Spring pins are designed for use in double shear applications.