Common Types of Screws
Screws and BoltsCredit: xandert http://morguefile.com/creative/xandert
More enduring and stronger than nails, screws have numerous advantages for the home carpenter. Particularly if the work must be dismantled for repair, cleaning, or packing, and ability to open the joint can be all important.
To use screws instead of nails is a lot more expensive in both time and money, but is often needed to meet requirements for great results. The main advantages of screws are (1) they supply more holding power, (2) they can be readily tightened to draw parts being fastened firmly together, (3) they are cleaner in appearance when correctly driven, id (4) they may be removed without damaging the material. The common wood screw is typically made from un-hardened steel, aluminum, stainless steel, or brass. The steel might be bright-finished or blued, or chrome-plated, or zinc-cadmium.
Wood screws are threaded by a gimlet point for roughly two-thirds of the length of the screw and bear a head slotted for driving using an inserted driver. Screws range in length from 1/4 inch to 6 inches. Screws up to 1 inch long step-up in size by eighths of an inch; screws 1 to 3 inches long step-up in size by quarters of an inch, and screws 3 to 6 inches long step-up by half inches.
Screws likewise vary in diameter as well as length of shaft. Each length is made in several shaft sizes designated by an arbitrary number that corresponds to no special measurement but suggests relative differences in diameter. Complete specifications for a screw involves type, material, finish, length, and screw size number. The last shows the wire gauge of the body, drill or bit size for the body hole, and drill or bit size for the starter hold.
The picking of the best shape for the screw to use depends on the function it must serve. A few common shape and sizes are as follows.
Flat head - The most popular, this screw can be counter-sunk, that is, screwed in until the head is flat with the surface of the stock, or somewhat below the surface.
Oval head - Though this type can be countersunk, and typically sunk to the rim, it normally protrudes a bit.
Round head - The head of this screw bulges out totally and is slightly decorative.
Fillister head - The head is formed like three checkers on top of each other so that it could be easily countersunk.
Bung head- The small head, not much broader than the shank, is comfortably countersunk.
Binding head- This has slightly tapering sides and a rounded top.
Lentil head -The head is formed like a small M & M candy.
Headless- The slot is recessed in the shank.
Truss head, or stove head - The head is wide and thin.
Pan head - The head is shaped like an inverted frying pan, narrower on the top, flat on top and bottom.
Drive - A steel, spiral knurl (an elevated twirl) is hardened so that the screw could be driven into soft metal.
Dovel -a wood screw having threads on both ends.
Winged - The head is wing-shaped (such as a bolt) so that it could be turned using your fingers.
Hanger bolt- -a wood screw on one end, a machine bolt on the other.