Types of Screws

There are a huge variety of fasteners for different jobs. It is a big job deciding on the right kind of fastener or screw and then finding it. Here is a pictorial guide I found on the internet [http://justpaste.it/7ux]. Looks pretty useful.

 The website of D. Lawless Hardware, an American company, provides a lot of information on screws in general. I have extracted some information from there website.

Basic Types of Wood Screws
Wood screws are classified by the type of drive, the shape of head, its length, and whether it is designed for wood or metal; this page refers to wood screws only.

Types of Drives
Drive refers to the indented shape on the screw head used to turn the screw. There are many different types of drives. Here we are only covering the four most used drives. These include slotted (flathead), phillips (crosshead), square, and pozidriv. A brief description of each drive is below with a picture at the bottom to illustrate each ones unique design.

SLOTTED/FLATHEAD: This is the original screw drive. You find these everywhere, though the practice of using screws with slotted drives is on the decline because the screwdriver slips out of the slot, particularly when you are applying heavy torque to really tighten down (or loosen, for that matter) these types of screws.

PHILLIPS/CROSSHEAD: This screw drive type is very popular - and again, you find them in a very wide range of applications. Common sizes are Phillips  #1, #2 and #3. The most common Phillips size is #2.

SQUARE: Square recess are being used more and more as they are very resistant to cam-out, which is a fancy way of saying the tip of the tool does not slip out and mar the screwhead very easily. Commonly found in two sizes: Square #2 and #3.

POZIDRIV: This screwhead isn’t seen very often in the U.S.A., though it is very common in Europe. It looks a lot like a Phillips screwhead, but it includes 4 more contact points. Common sizes are Pozidriv #1, #2 and #3.

Screw head types

In addition to the different types of drives, there are a variety of head designs, each meant for a particular kind of job. Flat head screws are typically found on wood screws that are usually countersunk, pan heads grip one part to another with considerable force and so on.

Screw Head Types

Threading and Point Types
Most wood screws have a common "pitch" to the treads, but some have a thread with a steeper incline. We simply call this a "fast" thread, but they are technically Type A screws.Think of this as a road going up a mountain; the steeper the road, the sooner you get to the top.
Also in reference to threads you will see "8-32". This is the common knob and pull screw thread. The "8" refers to the size (diameter) of the screw, and the "32" means it has 32 threads to the inch. Most of the screws for mounting hinges are self-tapping (they tap their own mating threads in wood) type AB (they have more threads per inch and are more effective in brittle materials like wood than Type A).

Threading on the shank is designed specifically for wood; wood threads have a tapped screw while sheet-metal screws have mainly a parallel thread. Wood type screws are also normally used for securing into wall plugs. Screws for chipboard usually have 2 threads the full length of the shank.

US Standards
One of the great things about the West is the standardising of most hardware items. Once standardised, there can be no confusion and tool can be built accroding to standard specifications. Here is a chart that shows standard screw sizes:

Indranil Banerjie
13 March 2012