Understanding Screw Heads and Drive Styles
Fastener Tech Data | Understanding Series Introduction
Screw type fasteners are manufactured with different head styles. Sometimes the style serves a functional purpose, and sometimes it's more decorative in nature. Understanding the differences will help you decide which style to choose.
There are two basic designs: countersunk and non-countersunk. Non-countersunk heads—where the head is fully exposed—encompass the largest variety. This style includes: binding, button, cheese, fillister, flange, hex, pan, round, socket and low socket, square and truss heads (binding head is occasionally referred to as binder head). Sometimes features are combined, as in the case of slotted hex, hex washer, slotted hex washer and round washer head designs.
Countersunk designs mainly consist of flat, oval and bugle heads. Unless the material is very soft, flat and oval heads require a countersunk hole. The advantage is that little or no part of the head protrudes beyond the surface of the material. If you are using flat heads screws in finish work, consider using a flat head screw cover (also known as a "beauty cap") to hide the head (not all drive styles will accept screw covers). Made of plastic, these caps are available in standard colors that match commonly used plastic laminates and wood. Bugle heads are commonly found in drywall screws, and the head design automatically compresses the drywall paper and gypsum as it is installed thus forming its own countersunk hole.
Drive style—or drive recess as it is called—refers to the kind of tool you use to install (or remove) the screw. Of the many that exist, the most common are: slotted, Phillips, combination (both slotted and Phillips), hex, hex socket, square, Torx® and spanner.
Use a slotted screwdriver (flat blade) for slotted, combination and one way screws; a Phillips screwdriver for Phillips and combination screws; a hex key for hex socket; and a Torx® driver for Torx® screws. To prevent head damage, match the driver to the screw head. For example, don't use a small slotted screwdriver with a large slotted screw, or the wrong size hex key. Depending on what size Phillips head screw you're using, you may need a No. 0, 1, 2, 3 or 4 Phillips screwdriver (the larger the number, the larger the driver tip). Probably the most prevalent are Nos. 1 and 2, although No. 0 will be needed for some very small screws and 3 and 4 for large screws. (See the Point / Bit Size Guide for information about Phillips, square and Torx® drive sizes, and the Socket Screw Products chart for information about hex key sizes.) Slotted and Phillips screwdrivers work with metric screws, but you must use metric hex keys with metric hex socket screws. Also, Phillips, square, hex and Torx® drive screws are popular because there's less chance for the driver to slip out and scratch finish work.
Hex head, like hex cap screws, require a wrench or socket. Use a wrench for square head bolts and screws.
If security is important—when you want to prevent someone from removing a screw—select an uncommon drive style. Square socket and Torx® offer a degree of security because those tools aren't as common. For improved security, consider using pin hex, pin Torx®, or spanner. Pin hex and pin Torx® are very identifiable—a small pin is added to the center of the drive hole. That means you will need to use special pin hex and pin Torx® drivers to install or remove those screws. One way screws are designed not to be removed, although a special removal tool is available.
For details about the bit, key or Phillips point size you will need for different screws, or screw head dimensions and other information, check out these reference charts…
Regardless of the screw head or drive style, chances are Fastener Mart has what you're looking for.