Alloy Steel
Socket Shoulder Screw
Socket shoulder bolts with a precision shoulder for pivots, levers, linkages, rollers and guide pins.
About the Socket Shoulder Screw
Shoulder bolts have a smooth, accurate shoulder between the head and thread, so parts can pivot or slide on them, for levers, linkages, rollers, pulleys and guide pins. They are alloy steel with a hex socket head: metric to ISO 7379 on 6 to 24mm shoulders with M5 to M20 threads (plus one 20mm zinc flake silver size), and imperial on 1/4 to 3/4 inch shoulders in UNC and 5/8 inch in BSW. Choose the shoulder size and length above; the guide below covers how they are measured, thread and hex key sizes, and fitting.
Also called shoulder bolts, pivot bolts or stripper bolts.
Features
- Shoulder acts as a pivot or locating dowel
- Hex-key drive
- High-tensile alloy steel, plain or zinc flake
Applications
- Pivots, levers and linkages
- Guide pins and rollers in machinery
What a shoulder bolt is
A socket shoulder screw has three parts: a round socket head, a plain cylindrical shoulder under the head, and a shorter, smaller thread at the end. The shoulder is the working part. A lever, link, roller or bushed part sits on the shoulder and turns or slides on it, while the thread screws into a tapped hole and the step between shoulder and thread pulls up tight against the face of the tapped part.
That is why people call them shoulder bolts, pivot bolts and stripper bolts. They are used for pivots, levers and linkages, guide pins and rollers in machinery, and as locating pins that can be removed.
How shoulder bolts are measured
A shoulder bolt is sized by the shoulder, not the thread: shoulder diameter x shoulder length, with the thread size that goes with that shoulder. The length is the shoulder only, from under the head to the step; the thread is extra. A 10 x 30mm shoulder bolt has a 10mm shoulder 30mm long and an M8 thread, which the selector shows as 10mmX30 with size M8.
Choose the shoulder diameter to suit the bore of the moving part, and a shoulder length a little longer than the thickness of the part (plus any washer) if it has to turn freely; if the shoulder is shorter than the part, tightening the thread clamps it.
Metric shoulder bolt sizes
Select a row to open that shoulder size in the selector and see every length.
Metric socket shoulder screws, ISO 7379, alloy steel. Shoulder diameter, thread (coarse pitch from Hobson's listing; Hobson's description gives no pitch for the zinc flake size), shoulder lengths in mm, thread length and hex key from Hobson's dimension tables. Pack is the minimum order quantity and varies with length. Tap a number to show it in the selector above.
| Shoulder | Thread | Shoulder lengths (mm) | Thread length (mm) | Hex key | Pack | Finish |
|---|---|---|---|---|---|---|
| 6mm | M5 x 0.8 | 10, 12, 16, 20, 25, 30, 40, 50 | 7.5 | 3mm | 25 to 50 | Plain |
| 8mm | M6 x 1 | 12, 16, 20, 25, 30, 40, 50, 60, 70 | 8.5 | 4mm | 25 to 50 | Plain |
| 10mm | M8 x 1.25 | 16, 20, 25, 30, 40, 50, 60, 70, 80 | 10 | 5mm | 25 | Plain |
| 12mm | M10 x 1.5 | 16, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100 | 12.5 | 6mm | 25 | Plain |
| 16mm | M12 x 1.75 | 30, 40, 50, 60, 70, 80, 90, 100, 120 | 14 | 8mm | 25 | Plain |
| 20mm | M16 x 2 | 40, 50, 60, 70, 80, 90, 100, 120 | 17.5 | 10mm | 10 | Plain |
| 20mm | M16 | 90 | 17.6 | 10mm | 10 | Zinc flake silver |
| 24mm | M20 x 2.5 | 50, 60, 70, 80, 90, 100, 120 | 21.4 | 12mm | 5 | Plain |
Imperial shoulder bolt sizes (UNC and BSW)
Imperial shoulder bolts follow the same rule: shoulder diameter x shoulder length, then the thread. Our UNC range is listed to ANSI B18.3 and the BSW range to BS 2470.
Imperial socket shoulder screws, alloy steel, plain finish. Shoulder diameter, thread, shoulder lengths in inches, and hex key from Hobson's dimension tables. Pack is the minimum order quantity and varies with length. Tap a number to show it in the selector above.
| Shoulder | Thread | Shoulder lengths (inch) | Hex key | Pack |
|---|---|---|---|---|
| 1/4 inch | #10-24 UNC | 3/8, 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 1-3/4, 2 | 1/8 inch | 25 |
| 5/16 inch | 1/4-20 UNC | 3/8, 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 1-3/4, 2, 2-1/4, 2-1/2 | 5/32 inch | 25 |
| 3/8 inch | 5/16-18 UNC | 3/8, 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 1-3/4, 2, 2-1/4, 2-1/2, 2-3/4, 3, 3-1/2, 4 | 3/16 inch | 25 |
| 1/2 inch | 3/8-16 UNC | 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 1-3/4, 2, 2-1/4, 2-1/2, 2-3/4, 3, 3-1/4, 3-1/2, 4, 4-1/4, 4-1/2, 5 | 1/4 inch | 10 to 25 |
| 5/8 inch | 1/2-13 UNC | 1-1/4, 1-1/2, 1-3/4, 2, 2-1/4, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, 5 | 5/16 inch | 10 to 25 |
| 3/4 inch | 5/8-11 UNC | 1-1/2, 1-3/4, 2, 2-1/4, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, 5 | 3/8 inch | 10 |
| 5/8 inch | 1/2-12 BSW | 1-1/4, 1-1/2, 1-3/4, 2, 2-1/4, 2-1/2, 2-3/4, 3, 3-1/2, 4, 4-1/2, 5 | 5/16 inch | 10 to 25 |
Strength marking: why it reads 012.9
Hobson lists the metric shoulder screws as class 012.9. In Hobson's Soko guide, a leading 0 in the head marking means reduced loadability: the material meets the property class, but the shape stops the screw reaching the full tensile capacity of that class. So do not treat it as a full strength class 12.9 bolt. Hobson publishes no load rating for joints made with these screws; for structural or safety critical joints, use the fastener your engineer specifies.
Plain or zinc flake?
- Plain: no coating. Hobson supplies plain fasteners lightly oiled to inhibit rust in the packet and help installation. For dry, indoor machine work, or where the part is oiled in service.
- Zinc flake silver (20mm shoulder x 90mm, M16): a 10 micron coating that Hobson rates for high corrosion resistance without any risk of hydrogen embrittlement, thin enough to mate with standard internal threads.
How to fit a shoulder bolt
- Drill and tap the fixed part for the thread size in the table, square to the face, deep enough for the full thread length.
- Fit the moving part (and any washer) over the shoulder.
- Screw the bolt in with a hex key or hex bit of the size in the table.
- Tighten until the step at the end of the shoulder seats on the face of the tapped part, then check the moving part turns or slides freely.
Shoulder bolts in Adelaide
Allmat supplies shoulder bolts, socket cap screws, grub screws and dowel pins to fitters, machine builders and maintenance crews across Adelaide and South Australia. Add them to a quote with the rest of your list and we will price the lot.
Shoulder bolts for machines and linkages
Socket shoulder screws, cap screws, grub screws and dowel pins are available to order from Allmat for fitters, machine builders, maintenance crews, toolmakers and trade across Adelaide and South Australia. Order through Allmat, we pick and pack it, then click and collect from the Allmat yard or have it delivered to site.
Goes with
Questions
Is a shoulder bolt the same as a shoulder screw?
Yes. Shoulder bolt, shoulder screw, socket shoulder screw, pivot bolt and stripper bolt all mean a socket head screw with a plain shoulder between the head and a smaller thread.
How do you measure a shoulder bolt?
By the shoulder: diameter x length, measured from under the head to the step. The thread is extra and is smaller than the shoulder. A 12 x 40mm shoulder bolt has a 12mm shoulder 40mm long and an M10 thread.
What thread goes with each shoulder size?
Metric: 6mm shoulder M5, 8mm M6, 10mm M8, 12mm M10, 16mm M12, 20mm M16 and 24mm M20. Imperial UNC: 1/4 inch shoulder #10-24, 5/16 inch 1/4-20, 3/8 inch 5/16-18, 1/2 inch 3/8-16, 5/8 inch 1/2-13 (or 1/2 BSW) and 3/4 inch 5/8-11.
What Allen key fits a shoulder bolt?
Metric: 3mm for the 6mm shoulder, 4mm for 8mm, 5mm for 10mm, 6mm for 12mm, 8mm for 16mm, 10mm for 20mm and 12mm for 24mm. The imperial sizes are in the table.
What are shoulder bolts used for?
Pivots, levers and linkages, guide pins and rollers in machinery, and removable locating pins: anywhere a part has to turn or slide on a plain shank rather than on a thread.
How strong is a shoulder bolt?
Hobson lists the metric range as class 012.9, where the leading 0 means reduced loadability: the shape stops it reaching the full tensile capacity of the class. Hobson publishes no load ratings for joints made with them, so for structural or safety critical joints use the fastener your engineer specifies.
How are shoulder bolts sold?
In packs of 25 for most sizes, 50 for a few lengths, 10 for the 20mm metric shoulder, the 3/4 inch shoulder and the longer imperial lengths, and 5 for the 24mm shoulder.
Where can I buy shoulder bolts in Adelaide?
Order through Allmat. Order ahead by phone on 1300 03 03 63 or send your list for a quote, then click and collect from 25 Kapara Road, Gillman, or have them delivered to site.
Socket Shoulder Screw: sizes and finishes we supply
150 lines by type and finish. Pick one above for its product code, pack sizes and dimensions.
| Head | Finish | Sizes | Lengths | Lines |
|---|---|---|---|---|
| Shoulder | Steel | 1/4, 5/16, 3/8, 1/2, 5/8, #10 | 1/4x1 to 3/4x5 (76 lengths) | 88 |
| Shoulder | Steel | M5, M6, M8, M10, M12, M16, M20 | 6mmX10 to 24mmX120 (61 lengths) | 61 |
| Shoulder | Zinc Flake Silver | M16 | 20mmX90 | 1 |
Data sheets and documents
The documents for the product you choose are listed with the selector above. Here is every Socket Shoulder Screw document from Hobson Engineering.
All Socket Shoulder Screw documents (5)
Data sheets and technical data (3)
Guides and articles (2)
Need them in bulk?
Add the sizes you need to your quote, or send us your list and we’ll price the lot and supply it with the rest of your order.
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