Special Shoulder Screw

Anatomy of a Shoulder Bolt

Engineers use the names shoulder screw and shoulder bolt for the same component. It carries a cylindrical shoulder ground to a controlled diameter, a wider head that spreads clamp load, and a shorter threaded section that anchors into a tapped hole. Each feature handles a separate mechanical job.

Most designs use a hex socket sunk into the head, so the screw seats flush and tightens inside tight pockets. The shear load path runs through the solid shoulder rather than the threads, which keeps the threaded portion clear of the radial forces that fatigue and crack an ordinary bolt.

Head and Drive: The head height and socket size determine tool access and seating depth. A correctly sized socket prevents cam-out during torquing, which protects both the fastener and the surrounding bore from damage on assembly lines that cycle thousands of parts a shift.

Material Grades and Sizing

Material choice decides how long a shoulder screw survives its working environment. UPS Lakshmi supplies the range in alloy steel hardened for strength and in stainless grades for corrosion duty, following ISO 7379 for metric sizes and ANSI B18.3 for imperial sizes, with grades SS-304, SS-316, and hardened alloy.

For wet or chemically aggressive service, 316 stainless steel shoulder bolts resist pitting far better than 304. Their corrosion resistance comes from added molybdenum in the alloy, which suits marine hardware and food-processing equipment. Where a lifting or tie-off point is needed, stainless steel shoulder eye bolts place a looped head on the same shouldered body.

Metric Sizing: Metric parts follow ISO 7379, so a 10 mm shoulder pairs with an M8 thread one increment below it. This relationship gives designers predictable clearance holes and lets a worn screw be swapped for an identical replacement without reworking the mating component.

Choosing the Right Shoulder Screw

Specifying the wrong part invites misalignment, premature wear, and unplanned line stoppages, so match the fastener to the duty before raising a purchase order. Run through these points first:

• Shoulder diameter and length checked against the clearance hole and the parts that pivot or slide on it
• Thread size and fit class, since a loose thread strips under repeated reversing load
• Material and finish chosen for the operating environment, from plain alloy steel through to 316 stainless
• Head and socket type matched to the available tool access and required seating depth
• Hardness and surface finish on the shoulder, which govern how fast the bearing face wears in service

A shoulder screw that holds its tolerance across a full service life protects the tooling and machinery built around it. Sourcing from an audited manufacturer with traceable material certificates and 65+ years of manufacturing expertise removes the guesswork that leads to field failures and avoidable warranty claims.

Share a drawing or request a sample lot to match the exact shoulder, thread, and grade your assembly calls for.

Shoulder Screw FAQs

What is the difference between a shoulder screw and a shoulder bolt?

There is no functional difference. Both terms describe the same part with a precise shoulder between the head and the thread. Catalog listings and standards use the names interchangeably, so a request for either will return the same fastener.

Which standard covers metric shoulder screws?

Metric shoulder screws follow ISO 7379, which fixes the shoulder diameter, length steps, and the matching thread size. Imperial parts follow ANSI B18.3. Working to a recognized standard keeps replacement parts interchangeable between suppliers and across production runs.

When should 316 stainless steel shoulder bolts be used?

Choose 316 when the part is exposed to salt, moisture, or chemicals, such as marine fittings, outdoor structures, or wash-down equipment. The molybdenum content resists pitting corrosion that would otherwise shorten the service life of a 304 screw, extending service life in environments where rust would otherwise require early replacement.

What drive type do shoulder screws use?

The common form carries a hex socket in the head, tightened with an Allen key. The recessed socket lets the screw seat flush and torque up inside confined pockets, which matters in jigs, fixtures, and moving assemblies with limited clearance around the head.

Are stainless steel shoulder eye bolts the same as a shoulder screw?

They share the shouldered body but differ at the head. A shoulder eye bolt replaces the flat head with a closed loop for attaching cables, slings, or springs, while the precision shoulder still acts as the locating or pivot surface.