There are a vast selection of woodscrews available for the DIYer to choose from. Below is a brief description of what is available in most DIY stores.
THE SCREW HEAD.
There are two common types of screw head, the first is the most popular one in use, that is the Phillips head or cross head as it is sometimes referred to, the second is the slotted head or straight / flat head, both are shown in fig 1 below.
There are others available such as security head screws which can only be turned using a Torx or star bit and there are anti vandal or one way screws which are very difficult to remove and are virtually a permanent fixing.
THE SCREW HEAD SHAPE
There are countersunk head screws which have a flat head which is tapered underneath to give a flush finish.
Roundhead screws have as you would expect a roundhead with a flat underside so when used as a fixing the head stays above the surface of the wood.
Another head shape is the oval which has a less prominent rounded head and is tapered underneath, these could be used as an example for fixing brass door handles in place.
Gauge refers to the width of the screw thread, typical sizes are 6s, 8s, 10s, 12s gauge so the higher the gauge the thicker the screw thread.
The length of the screw is measured from the tip of the screw to the underside of the head, typical lengths available are from 1/2 inch (12mm) to 4 inches (100mm) long.
Woodscrews are usually made from hardened steel or brass and can be purchased with an anti-corrosion finish if required. Below are photos of various woodscrews available at most DIY stores, B & Q, Wickes, Focus, etc.