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Shoulder Bolts

Shoulder bolts are used as bearings and spacers. Their applications number many: as shafts for cam rollers and other rotating parts, as pivots and stud bolts, and as bearing pins for swing arms, links and levers. Often combined with bronze sleeve (Oilite) bearings, they are also used as a guide in blanking and forming presses and in punch and die operations. Shoulder bolts have a cylindrical head, a smooth cylindrical shoulder and a short threaded section. A small area between the threads and shoulder is undercut, which allows for a tight fit against the mating surface. They are also known as: 

stripper bolts, axle bolts, shoulder screws, hexagon socket head shoulder screws.

 Shoulder bolts are used with nuts and internally threaded (tapped) holes.

Threads are standard right-hand and Unified inch coarse series (UNC, Unified National Coarse). Their point is flat or slightly concave and chamfered.

Typically, shoulder bolt sizes range from 1/4" to 3/4" in diameter, and lengths span from about 3/8" to 6". Size is the shoulder diameter and length is the length of the shoulder—measure length from under the head to the end of the shoulder. An additional dimension is thread size, which is always smaller in diameter than the shoulder, and ranges from 10-24 to 5/8-11 for the common sizes. Thread length is fixed for each size.

"Shoulder refers to the enlarged unthreaded portion of the screw, the diameter of which serves as the basis for derivation of the nominal size." The shoulder is precisely sized and is between -0.002" and -0.004" of the nominal size. So, for a 1/2" (0.5000") shoulder bolt, the shoulder diameter will be 0.498" maximum to 0.496" minimum.

Shoulder bolts have a hex socket head so tighten using a hex driver. For sizes 1 1/4" and smaller, hex socket size is half of the shoulder diameter; for 1 1/2" to 2" sizes, it's a little larger than half. Being internally wrenched, clearance around the head for a wrench is not needed so they can be installed in a counterbored recess. Table 1 lists head diameter and height, hex socket size and thread size and length.

Steel, plain finish, is the standard material and finish (plain finish is unplated so there is no surface treatment to inhibit rust).

Refer to American Society of Mechanical Engineers Standard ASME B18.3, Socket Cap, Shoulder, Set Screws, Hex, and Spline Keys, for specifications relating to shoulder bolts.

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