Socket Head Shoulder Screw

Shoulder Bolts — Precision Ground, Socket Head, Alloy Steel

Shop Shoulder Bolts

Shoulder bolts — also called shoulder screws, stripper bolts, or socket head shoulder screws — are a specialized fastener where the function is provided by the body, not the threads. A cylindrical shoulder, precision-ground to a controlled diameter and length, extends between the head and a shorter threaded shank. A bearing, bushing, or mating component rides on the shoulder; the threads simply anchor the bolt in place. Shoulder bolts conform to ASME B18.3 for inch series.

Understanding Shoulder Bolt Dimensions

Three dimensions define a shoulder bolt — and all three must be specified correctly:

Shoulder Diameter is the precision-ground body diameter. This is the controlling fit dimension — the bore in the mating component (bushing, bearing, pivot block) must match the shoulder diameter. Shoulder diameters are machined to a close h6 tolerance for accurate fit.

Shoulder Length is the length of the unthreaded ground body, measured from under the head to the start of the threads. This controls the spacing, pivot travel, or stack height in the assembly. Shoulder length must equal or slightly exceed the thickness of the component being pivoted or guided — if the shoulder is too short, the component will bind; if too long, it will have excess play.

Thread Size is always smaller than the shoulder diameter — the threaded shank does not protrude beyond the shoulder body. Standard inch relationships are fixed: a 1/4" shoulder uses 10-24 threads; 5/16" shoulder uses 1/4-20; 3/8" uses 5/16-18; 1/2" uses 3/8-16; 5/8" uses 1/2-13; 3/4" uses 5/8-11; 1" uses 3/4-10.

Common Applications

Shoulder bolts are workhorses in tooling and precision machinery. In stamping dies and press tooling, they guide stripper plates — the plate travels up and down on the shoulder body, which provides accurate alignment. In jigs and fixtures, shoulder bolts act as pivot pins for clamps and swing arms. In cam-follower assemblies, a shoulder bolt provides the precision pivot shaft. In robotic and automation equipment, they locate components that must be repeatedly removed and repositioned with accuracy. Wherever a precision pivot, guide, or spacer is needed in a threaded-hole assembly, a shoulder bolt is the standard solution.

Shoulder Bolt vs. Dowel Pin

Both shoulder bolts and dowel pins provide accurate location, but they serve different functions. A dowel pin is a press-fit or close-clearance locating pin — it locates parts relative to each other but does not clamp them. A shoulder bolt pivots or guides a moving component while anchoring itself via its threaded shank. Use dowel pins when you need to locate two static parts relative to each other; use shoulder bolts when a component must pivot, travel, or be repeatedly removed from a precise location.

Material and Finish

Standard shoulder bolts are alloy steel, heat treated, with a black oxide or plain finish. The shoulder is precision ground after heat treatment to maintain dimensional accuracy. Stainless steel shoulder bolts are available in 18-8 for corrosive environments — note that the ground shoulder tolerance is the same, but the lower hardness of stainless may limit use in high-wear pivot applications without a bushing or bearing insert.

Frequently Asked Questions

What is the difference between a shoulder bolt and a shoulder screw?
They are the same fastener — "shoulder bolt" and "shoulder screw" are interchangeable terms used in different industries. "Shoulder bolt" is more common in tooling and die work; "shoulder screw" appears in precision machinery and robotics. "Stripper bolt" refers specifically to the application in stamping die stripper plates.

How do I size a shoulder bolt for a pivot application?
The shoulder diameter must match the bore in the pivot component (bushing, bearing, or direct bore). The shoulder length must match or slightly exceed the thickness of the pivoting component. The threaded end must engage enough thread in the mounting hole to hold — minimum 1.5× thread diameter engagement is a common guideline.

Can I use a shoulder bolt as a dowel pin?
In some applications, yes — if you need a locating pin that is also captivated by threads, a shoulder bolt works. However, shoulder bolt tolerances (h6) are generally looser than precision dowel pin tolerances (h6 to m6 interference), so a shoulder bolt will not provide the same location accuracy as a press-fit dowel in a matched reamed hole.

What socket (hex key) size do shoulder bolts use?
Shoulder bolts use the same hex key as socket head cap screws of the same shoulder diameter: 1/4 inch shoulder uses 3/32 inch hex key (10-24 threads); 5/16 inch uses 5/32 inch; 3/8 inch uses 7/32 inch; 1/2 inch uses 9/32 inch; 5/8 inch uses 3/8 inch; 3/4 inch uses 7/16 inch; 1 inch uses 9/16 inch. Verify with fastener specification — hex key sizes may vary by manufacturer.

Shoulder bolts are frequently used alongside dowel pins, socket head cap screws, and flat washers in jig, fixture, and tooling assemblies. For pivot and guide applications requiring a press-fit location rather than a threaded anchor, see our dowel pins and roll pins. The complete socket fastener family — including socket head cap screws, flat head socket cap screws, button head cap screws, and socket set screws — is available through the Sockets category.