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Wood vs. Metal Threading, Dimensions, and Types of Heads

Screws are basically of two types:
  • wood screws are intended for wood and other soft materials. They have a lower depth on the thread, and the threads are further apart. Between the screw head and the threads there is an plain, unthreaded portion of the shaft called the shank.
  • metal screws have deeper ridges that are closer together and extend all the way from the tip to the head . They are intended for use with thin, strong materials like sheet metal.
Screws come in:
  • lengths generally from one-quarter to three inches, though lags can be much longer. When joining two pieces, about a third of the screw should pass through the top piece and the remainder be anchored in the base.
  • sizes of the diameter of the central shaft, called the gauge, measured at the shank, the smooth part just underneath the head but before the threads, from #0 (about one-sixteenth of an inch) to #20 (about five-sixteenths of an inch)
The most common types of heads are:
  • round head screws are what people commonly think of as a screw, with semicircular top caps and a flat rim that fits up against the top material and may allow it to slide about the anchoring shank
  • flat heads are level across the top and beveled down to the shank and designed to fit flush with the surface down into a V-shaped hole countersunk into the material.
  • oval head screws resemble flat heads but that the top of the screw is rounded slightly to give the screw a neater, finished look
  • pan heads resemble nail heads in order to clasp the top material

  • hex heads tops are shaped like bolt heads so that hex or socket drivers can turn them as easily as screwdrivers

Go to the prior page on screws.

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