Custom Shoulder Bolts and Shoulder Screws

What makes a shoulder bolt a custom shoulder bolt?

A shoulder bolt has three sections: the head, the shoulder and the thread. It is specified by shoulder diameter and shoulder length, so a 3/8 × 2 shoulder bolt has a 3/8 in. shoulder 2 in. long, and its overall length is the head height plus the shoulder plus the thread, a different way to call out a bolt (source 1). In the inch series the thread is smaller than the shoulder, 5/16-18 under a 3/8 in. shoulder (source 2). Shoulder bolt and shoulder screw are the same part. Range bolt and stripper bolt are shoulder bolts named for the job they do in a mold (source 1).

A shoulder bolt is custom when the catalog has one thing wrong for you: a shoulder diameter between or outside the standard sizes, a shoulder length nobody lists, another thread or thread length, a head height or diameter, or a material. For metric shoulder screws, ISO 7379 covers nominal shoulder diameters from 6.5 mm up to and including 25 mm (source 3). Jim Fattori, writing in Plastics Technology, says there are times “when you have to make a custom shoulder bolt in order to satisfy a problem when a standard size is not available,” usually one that needs a very long shoulder (source 1). In a mold, he writes, “standard shoulder bolts don’t often come in the exact length you want,” so a longer one gets used and can create a problem with the molding machine’s daylight (source 4).

Sizes are quoted down to M1. For larger sizes, send the print. A plain pin with no thread is on shafts and pins, and the rest of the family is under custom screws, bolts and studs.

What goes on the print of a shoulder bolt?

The shoulder is the working part. Eugene Fastener, a fastener distributor, calls it “the functional element of the fastener” (source 2). Each row below is a callout the quote needs and what it decides.

The shoulder, the relief and the runout

A shoulder that runs as a bearing surface is the usual reason for a ground callout; Fattori calls it a journal when it acts as a shaft for a bushing or bearing (source 1). A ground shoulder is quoted with precision grinding. Typical machined tolerance is ±0.005 in, ±0.001 in on critical turned diameters, and down to ±0.0002 in on wire-EDM and other finished features; ground features are quoted to ±0.0001 in. Threads are quoted to the class on the print. The shoulder, relief and head are turned features, and CNC turning covers the diameter and tolerance bands.

The relief is where an over-tightened shoulder bolt most likely breaks. Fattori calls the thread neck “the weakest point of a shoulder bolt” and says an over-torqued one “will most likely fracture at this location” (source 1). BAER Tools, a tooling company, adds that the rounding of a relief has “a direct impact on notch effect” (source 6). Name the DIN 76 form on the print, or give the relief’s diameter, width and radius.

If the shoulder has to run true to the thread, put the callout on the print. Position, perpendicularity and runout callouts are quoted from the print. ISO 7379 gives geometrical tolerances for a catalog bolt (source 3); a custom bolt takes the ones on your print.

Where shoulder bolts go: pivots, guides, stops and stripper bolts

Eugene Fastener lists the uses: pivot pins for links, cams, rocker arms and levers where a part turns on the shoulder, linear guides in small mechanisms, standoffs where the shoulder length sets the gap, and stop pins (source 2). In most of these one of two numbers does the job: the shoulder diameter for the fit, or the shoulder length for the gap or stack height. Those are the two to get right on the print.

In a die the same part is a stripper bolt. It guides the stripper plate, the shoulder controls travel, a spring bears against the head, and its length specification is “critical to set stroke” (source 2). In a mold Fattori splits the names: a range bolt limits how far a plate or mold component travels, and a stripper bolt or puller bolt pulls one. Range bolts are almost always used in three-plate molds and are also used in stripper-plate molds (source 4).

Side load is what hurts them. Fattori writes that range bolts “are not designed to have a side load applied to them … but they often do,” and that with the thread neck so much smaller than the rest of the bolt, “it will not take a lot of force for it to fail at that location” (source 4). Say in the part description what the bolt does (pivot, guide, stop or stripper), and the free design review that comes with every quote reads the print against that job.

Which material and hardness for a custom shoulder screw?

Eugene Fastener names alloy steel as the standard choice for machine tool, industrial and tooling use, and 18-8 stainless for food processing, washdown, outdoor assemblies and chemical exposure (source 2). A print can call for titanium, 304, 316, brass, bronze, or hardened steel heat treated to the hardness on the print. The grade pages cover titanium, 304 stainless, 316 stainless, brass and steel. Other alloys and plastics quoted on request. Name the grade on the print.

Zinc plating, black oxide and heat treat are quoted with the part. Zinc plating on hardened steel is where hydrogen embrittlement comes in, and that is covered next.

Does plating a hardened shoulder screw risk hydrogen embrittlement?

Randy Lammers of Würth Industry North America writes that “hydrogen atoms are introduced to the steel in high concentrations during the pre-cleaning and electrolytic process of applying metallic materials (commonly, zinc),” and that “a delayed failure occurs one to 48 hours after fastener installation, once sufficient stress has been applied” (source 7).

He quotes the introduction to ASTM F1941, which names “a risk of delayed failure due to hydrogen embrittlement for case hardened fasteners and fasteners having a hardness above 39 HRC,” says the risk “cannot be completely eliminated,” and concludes that “the application of a metallic coating by electrodeposition is not recommended for such fasteners” (source 7). The Wikipedia article on hydrogen embrittlement calls baking “commonly used after electroplating,” though “not always fully effective because a sufficient time and temperature must be reached” (source 8).

Baking after plating is quoted when the print calls for it. Whether to plate a hardened screw at all is the print’s call, and the quote follows the print. Put the plating, the bake and the hardness on the print together so the quote shows the added step.

What to send: a print, a sketch or a new sample part

A dimensioned print with the items in the table above is the quickest way in. Files: Any file type; STEP + PDF ideal. A fully dimensioned 2D PDF is quoted without a CAD line. With no print, send a hand sketch with the dimensions you know, the bore the shoulder runs in, the thickness of any plate it holds, what the thread goes into and the travel or stack height it has to set, and the quote lists what is still missing. A drawing made from a sketch is quoted as its own line on the first order. If a worn or broken part is the only one left, send photos and a description first and the reply says what to send.

A new sample part also works. Send a new part, not the worn one. Wear changes the sizes that matter. The sample ships back with the parts. It is measured and drawn through reverse engineering; the drawing made from the sample is quoted as its own line on the first order, and reorders come off the same drawing. An unused spare works the same way. Parts are supplied as replacements by fit and dimensions. No OEM logos, part numbers or markings are copied.

Quantities, reorders and blanket orders

Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each. 25 pieces is a good start. At 200, the price per part drops a lot. Small-batch CNC machining covers how quantity works.

Reorders at the same revision: send the last quote or PO number and it’s requoted. A year’s usage, stripper bolts for a die you rebuild on a cycle for example, can be quoted as a blanket order delivered in releases. Price, release schedule and lead time per release are set in the quote.

How long do custom shoulder bolts take?

Quotes come back in 24-48 hours. Rush: 1-2 weeks. Standard: 4-6 weeks (typical). Extended: 6-8 weeks, for jobs that aren't time-sensitive. Rush 1-2 weeks applies to machined parts with no secondary operations. Heat treat, grinding, EDM and finishing add time, and the quote gives the real date. A ground shoulder, a hardness callout and plating each fall under that sentence. Lead time starts at order approval. Put your need date in the part description and the quote answers it. For a machine that is down, see rush CNC parts.

What comes with the parts

Every part is inspected against your print before it ships. If a part doesn’t match the print, it’s remade or credited. No C of C or material certifications ship with parts by default. If your PO needs them, say so before the quote. Inspection reports on critical dimensions aren’t included by default. If you need one, ask when you place the order.

Studs are on custom studs, and fasteners in Whitworth, BSF, BA and pre-unified American threads are on obsolete-thread fasteners.

Sources

Quoted passages on this page come from the following, all accessed 29 September 2026. Where anything here differs from your print, the print governs.

1. Jim Fattori, “Why Shoulder Bolts Are Too Important to Ignore (Part 1),” Plastics Technology, June 2019: ptonline.com/articles/shoulder-bolts-why-theyre-too-important-to-ignore-part-1 (head, shoulder and thread; how a shoulder bolt is specified; shoulder diameter and length figures; journal; thread neck; radius under the head; thread engagement; custom bolts when a standard size is not available).

2. Eugene Fastener, “Shoulder Bolt Selection Guide,” undated, eugenefast.com/home/page/resources/shoulder-bolt-selection-guide (shoulder as the functional element; inch shoulder and thread pairing; shoulder diameter and length; thread smaller than shoulder; uses; stripper bolt; materials).

3. Industrial Fasteners Institute, “ISO 7379:1983, Hexagon socket head shoulder screws,” undated: indfast.org/product/iso-73791983-hexagon-socket-head-shoulder-screws (nominal shoulder diameters from 6.5 mm up to and including 25 mm; geometrical tolerances).

4. Jim Fattori, “Why Shoulder Bolts Are Too Important to Ignore (Part 2),” Plastics Technology, July 2019: ptonline.com/articles/part-2-why-shoulder-bolts-are-too-important-to-ignore (exact lengths; range, stripper and puller bolts; side load and the thread neck; shoulder-to-thread concentricity; clearance and counterbore; wrench flats).

5. Ondrives.US, “Custom Shoulder Screws,” undated, ondrivesus.com/custom-shoulder-screws (undersize diameter and oversize shoulder length for free rotation).

6. BAER Tools, “Thread Relief Explained: Function, DIN 76 & Practical Use,” 28 May 2025, baer.tools/en/blog/thread-relief-what-is-it-actually (thread relief defined; DIN 76 forms A to D; width about three times the pitch; rounding and notch effect).

7. Randy Lammers, Würth Industry North America, “A practical understanding of hydrogen embrittlement and fastener failure,” Design World, 5 May 2022: designworldonline.com/a-practical-understanding-of-hydrogen-embrittlement-fastener-failure (hydrogen introduced in plating; delayed failure; the ASTM F1941 introduction and its conclusion).

8. Wikipedia, “Hydrogen embrittlement”: en.wikipedia.org/wiki/Hydrogen_embrittlement (baking after electroplating, and its limits).