Last update: Dec. 23, 2000

©By: John T. Blair (WA4OHZ)
1133 Chatmoss Dr.,
Va. Beach, Va. 23464; (757) 495-8229

Ever wonder what the different type bolt heads were called? What about the various types of nuts?

While I know the difference between a flat and pan head bolt, I didn't know what many of the others bolts are called, that we use every day. After digging around for quite some time, I've managed to piece together the following information from various sources. I hope it saves you some time and is of help.

Bolt Heads
	Pan Head - Recommended for new designs to replace round, truss and binding heads. Provides a low large diameter head, but with characteristically high outer edge along the outer perphery of the head where driving action is most effective for high tightening torques.
	Flat Head - Has an angle of 80 to 82 degrees. Used where finished surfaces require a flush face. Requires hole be countersunk and offers good centering.
	Round Head - Was the common used in the past. Is being replaced with other type heads in newer designs.
	Oval Head - Requires that the hole be coutersunk. This bolt gives a more attractive appearence than the traditional round head bolt.
	Fillister Head - This bolt has a smaller diameter head than the round head. The head is also taller, consiquently it has a deeper slot. The smaller diameter head increases the pressure applied on a smaller area and allows for assembly closer to flanges and raised surfaces. In addition, the mounting hole can counterbored.
	Binding Head - This bolt is generally used in electrical and radio work because its undercut head binds and elminates fraying of stranded wire. It is an attractive bolt, has a medium to low head.
	Truss Head - Also called oven, stove, or oval binding head. It has a low head, and a large diameter. It can be used to cover large diameter clearance holes in sheet metal, where additional play is necessary during assembly.
	Holt Head - This bolt is a tamper proof type bolt. It is also very decorative. It requires a special tool for installation and removal.
	One-way Head - As the name suggests, once it is installed it can't be removed. It is installed with a standard flat blade screwdriver.
	Phillips Finishing Washer Head - Very nice appearance for electronic and appliance uses.
	Washer Head - Has the finished appearance of the conventional round head plus a wahser. Created to provide extra large bearing surface under the head. The Truss head is the replacement for this bolt.
	Undercut Head - Comes in both flat and oval head. Very similar to them both, but the lower 1/3 of the countersunk portion is removed.
	Square Shoulder Screws - An adaptation of the carriage bolt. It has a truss head on a square shank - to resist rotation.
	Indented Hexagon - An inexpensive wrench head fastener. Made to standard hexagon head dimensions. These bolts have an identifying depression on their heads.
	Hexagon Washer Head - Same as indented hexagon head, except it has a washer section on its base to protect the inderlying part from wrench damage.
	Acron Head - Very nice looking trim screw, used for appliance applications.
	Hexagon Head (Trimed) - This is the standart type bolt. Used for general applications.
	Welding Screw - Developed to privide a strong permanent threaded fastener which becomes an integral part of the assembly. It uses the principle of proection welding by means of multiple lubs on the head surfaces.
	Flat Head Welding Screw - Takes advantage of the self- centering offered by the countersunk portion and provides a flush top surface.
	T (overlug) Welding Screw - For applications requiring a smooth finished outer surface.

On to Nut Types.

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