ISO 7379 Shoulder Screws
Shoulder 6.5 – 25 mm · M5 – M20 · 12.9The metric standard, with an f9 ground shoulder and a socket head, plain or knurled. We also make the common commercial series with 4 to 24 mm shoulders.
ISO 7379 Socket Shoulder Screws & ASME B18.3 Stripper Bolts: Manufacturer & Exporter
A shoulder bolt has a socket head, a ground plain shoulder and a short thread of smaller diameter. When it is tightened, the shoulder face seats on the base part and the shoulder stays free and accurate, so a lever, roller, bushing or plate can turn or slide on it.
Exotic Alloy manufactures shoulder screws in Mumbai, India, to ISO 7379 and ASME B18.3. Blanks are headed or turned, heat treated, and the shoulder is centreless-ground after hardening, so it is round, straight and in tolerance. Threads are rolled, and the shoulder face and thread undercut are machined so that the screw seats squarely. We supply machine builders and toolrooms in India, and export to Germany, Europe and the Americas.
Custom Sizes
Standard ISO 7379 and inch sizes in 12.9 black oxide are supplied from stock. Special shoulder lengths and diameters, tighter shoulder tolerances, stainless and exotic alloys, hex-head versions and drilled or slotted shoulders are made to drawing.
Shoulder 4 – 25 mm
¼ – 1½″ inch
f9 or tighter
Plain or knurled head
12.9, SS 304, alloys
Shoulder bolt at a glance
- Head
- Cylindrical socket head, plain or knurled
- Shoulder
- Ground plain diameter; metric f9, inch 0.002–0.004″ under nominal
- Thread
- Smaller than the shoulder, with an undercut so the shoulder seats flat
- Length
- Nominal length = shoulder length only
- Standards
- ISO 7379 (metric), ASME B18.3 (inch)
- Related
- Socket head cap screws, Allen bolts
Shoulder Bolt Specification
The range we manufacture and supply.
StandardsISO 7379 hexagon socket head shoulder screws; ASME B18.3 inch socket head shoulder screws; ISO 286 f9 shoulder tolerance; ISO 898-1 class 12.9
Size rangeShoulder 4 to 25 mm with M3 to M20 thread; inch ¼″ to 1½″ shoulder; shoulder lengths from 4 mm and ¼″
ShoulderCentreless-ground after heat treatment; f9 standard; h7, g6 or customer tolerance on request; length tolerance +0.25 / 0 mm as standard
ThreadISO metric coarse 6g; UNC / UNF 3A for inch; rolled; thread undercut next to the shoulder face
GradesMetric class 12.9 (1220 MPa); inch alloy steel 140 ksi tensile, HRC 32–43; AISI 304 stainless; 316, 17-4PH and alloys to drawing
FinishBlack oxide and oil (steel); plain; passivated stainless; nickel or zinc-nickel to order
HeadSocket head, plain or knurled; hex head and slotted head versions to drawing
CertificationEN 10204 3.1 with heat number, hardness and shoulder diameter record; PMI for stainless
MarkingMaker's mark and property class on the head where size allows
PackingOiled and boxed by size; ground shoulders protected in individual sleeves or trays for precision lots
Types of Shoulder Bolts We Manufacture
ASME B18.3 Inch Shoulder Screws
¼ – 1½″ · alloy steel · HRC 32–43The inch series, with the thread one step smaller than the shoulder and the shoulder ground 0.002 to 0.004″ under nominal.
Stripper Bolts
Press tools & diesShoulder screws that guide and retain spring-loaded stripper plates. Their shoulders are matched in length so the plate stays level.
Precision Shoulder Screws
h7 · g6 · custom toleranceTighter-tolerance shoulders for bearings, cam followers and indexing mechanisms where f9 clearance is too loose.
Stainless Shoulder Bolts
AISI 304 · 316 · 17-4PHFor food, packaging and medical machines and for wash-down areas. 17-4PH is used where stainless must also be hard.
Hex Head & Special Shoulder Bolts
To drawingHex or flanged heads, cross-drilled shoulders for lubrication, and long or stepped shoulders for linkages and conveyors.
Shoulder Bolt Dimensions: ISO 7379 & ASME B18.3
ISO 7379 as published, the commercial metric series most catalogues stock, and ASME B18.3 inch sizes.
| Thread d | Pitch P | Shoulder ds f9 limits, mm | Thread length b max | Head dk max | Head k max | Hex key s | Key depth t min |
|---|---|---|---|---|---|---|---|
| M5 | 0.8 | 6.5 (-0.013 / -0.049) | 9.75 | 10 | 4.5 | 3 | 2.4 |
| M6 | 1 | 8 (-0.013 / -0.049) | 11.25 | 13 | 5.5 | 4 | 3.3 |
| M8 | 1.25 | 10 (-0.013 / -0.049) | 13.25 | 16 | 7 | 5 | 4.2 |
| M10 | 1.5 | 13 (-0.016 / -0.059) | 16.4 | 18 | 9 | 6 | 4.9 |
| M12 | 1.75 | 16 (-0.016 / -0.059) | 18.4 | 24 | 11 | 8 | 6.6 |
| M16 | 2 | 20 (-0.020 / -0.072) | 22.4 | 30 | 14 | 10 | 8.8 |
| M20 | 2.5 | 25 (-0.020 / -0.072) | 27.4 | 36 | 16 | 12 | 10 |
Dimensions in mm from ISO 7379. The f9 limits in brackets are our calculation from ISO 286.
| Shoulder d1 mm | f9 limits mm | Thread | Head dia. mm | Head height mm | Thread length mm | Hex key mm | Shoulder length tol. mm |
|---|---|---|---|---|---|---|---|
| 4 | -0.010 / -0.040 | M3 | 7 | 3 | 7 | 2 | +0.25 / 0 |
| 5 | -0.010 / -0.040 | M4 | 9 | 4 | 8 | 2.5 | +0.25 / 0 |
| 6 | -0.010 / -0.040 | M5 | 10 | 4.5 | 9.5 | 3 | +0.25 / 0 |
| 8 | -0.013 / -0.049 | M6 | 13 | 5.5 | 11 | 4 | +0.25 / 0 |
| 10 | -0.013 / -0.049 | M8 | 16 | 7 | 13 | 5 | +0.25 / 0 |
| 12 | -0.016 / -0.059 | M10 | 18 | 9 | 16 | 6 | +0.25 / 0 |
| 16 | -0.016 / -0.059 | M12 | 24 | 11 | 18 | 8 | +0.25 / 0 |
| 20 | -0.020 / -0.072 | M16 | 30 | 14 | 22 | 10 | +0.25 / 0 |
| 24 | -0.020 / -0.072 | M20 | 36 | 16 | 27 | 12 | +0.25 / 0 |
The series most standard-parts catalogues stock, with 6, 12 and 24 mm shoulders in place of ISO's 6.5, 13 and 25, plus M3 and M4 sizes. Say which series you need when ordering.
| Nominal | Shoulder D max / min, in | Thread | Head A max / min, in | Head H max / min, in | Hex key J | Key depth T min, in | Thread length E in |
|---|---|---|---|---|---|---|---|
| 1/4″ | 0.2480 / 0.2460 | #10-24 | 0.375 / 0.357 | 0.188 / 0.177 | 1/8″ | 0.094 | 0.375 |
| 5/16″ | 0.3105 / 0.3085 | 1/4-20 | 0.438 / 0.419 | 0.219 / 0.209 | 5/32″ | 0.117 | 0.438 |
| 3/8″ | 0.3730 / 0.3710 | 5/16-18 | 0.562 / 0.543 | 0.250 / 0.240 | 3/16″ | 0.141 | 0.500 |
| 1/2″ | 0.4980 / 0.4960 | 3/8-16 | 0.750 / 0.729 | 0.312 / 0.302 | 1/4″ | 0.188 | 0.625 |
| 5/8″ | 0.6230 / 0.6210 | 1/2-13 | 0.875 / 0.853 | 0.375 / 0.365 | 5/16″ | 0.234 | 0.750 |
| 3/4″ | 0.7480 / 0.7460 | 5/8-11 | 1.000 / 0.977 | 0.500 / 0.490 | 3/8″ | 0.281 | 0.875 |
| 1″ | 0.9980 / 0.9960 | 3/4-10 | 1.312 / 1.287 | 0.625 / 0.610 | 1/2″ | 0.375 | 1.000 |
| 1-1/4″ | 1.2480 / 1.2460 | 7/8-9 | 1.750 / 1.723 | 0.750 / 0.735 | 5/8″ | 0.469 | 1.125 |
| 1-1/2″ | 1.4980 / 1.4960 | 1-1/8-7 | 2.125 / 2.095 | 1.000 / 0.980 | 7/8″ | 0.656 | 1.500 |
ASME B18.3 socket head shoulder screws, dimensions in inches. Standard shoulder lengths run from ¼″ to ¾″ in ⅛″ steps, from ¾″ to 5″ in ¼″ steps, and in ½″ steps above 5″.
Shoulder Tolerance & Fit Calculator
The shoulder is always smaller than nominal, so it slides into a nominal-size bore with a predictable running clearance. Choose the bore tolerance to set how loose the fit is.
Fit calculator
Metric limits from ISO 286 (H bore: 0 / +IT). Inch bore taken as nominal to nominal + your value. Clearance = bore − shoulder.
Result for 10 f9 / H8
0.013
mm min. clearance
0.071
mm max. clearance
Shoulder:9.951 – 9.987 mm
Bore:10.000 – 10.022 mm
Shoulder Bolt Grades & Mechanical Properties
| Grade | Basis | Tensile min | Yield min | Hardness | Other |
|---|---|---|---|---|---|
| Class 12.9 | ISO 898-1 (metric) | 1220 MPa | 1100 MPa | 39–44 HRC | Black oxide; the standard ISO 7379 grade |
| Inch alloy steel | ASME B18.3 | 140 ksi (965 MPa) | 120 ksi (827 MPa) | HRC 32–43 | Elongation 15 % min, reduction of area 45 % min |
| AISI 304 | Stainless | Per bar condition and agreed class (e.g. A2-70) | – | Non-hardenable; for corrosion, not wear | |
| 17-4PH | Precipitation-hardening stainless | Per heat treatment condition (H900–H1150) | 40 HRC min in H900 (ASTM A564) | Stainless with a hard, wear-resistant shoulder | |
The thread is the weak point, not the shoulder. The thread is smaller than the shoulder and sits right next to the undercut, so tension strength is set by the thread, and seating torque is limited by the small shoulder face. Do not tighten a shoulder screw to the torque of a cap screw of the same grade.
Shoulder Bolt Materials
Every grade links to its datasheet on this site.
Hardenable stainless
17-4PH / 416 / 440CStainless with a hard, wear-resistant shoulder.
Special alloy shoulder bolts: minimum properties of the bar we make them from
| Alloy | UNS | Condition supplied | Tensile min MPa | Yield 0.2 % min MPa | Elongation % | Why it is chosen for hex bolts |
|---|---|---|---|---|---|---|
| Inconel 625 | N06625 | Solution annealed (Grade 1) | 827 | 414 | 30 | Seawater, sour gas, cryogenic to 980 °C oxidation; subsea flange bolting |
| Inconel 718 | N07718 | Solution treated + aged (AMS 5662) | 1240 | 1035 | 12 | Highest strength to 650 °C; turbine and wellhead bolting |
| Monel 400 | N04400 | Hot-finished annealed | 517 | 207 | 35 | Seawater, hydrofluoric acid, no chloride SCC; marine and valve bolting |
| Monel K-500 | N05500 | Age hardened (AMS 4676) | 960 | 690 | 18 | Monel 400 corrosion resistance with three times the yield; pump shafts, subsea |
| Hastelloy C-276 | N10276 | Solution annealed (ASTM B574) | 690 | 283 | 40 | Wet chlorine, hot acids, mixed oxidising / reducing media; chemical reactors |
| Incoloy 825 | N08825 | Annealed (ASTM B425) | 586 | 241 | 30 | Sulphuric and phosphoric acid, sour gas (NACE MR0175); pickling plant |
| Duplex 2205 | S32205 | Solution annealed | 655 | 450 | 25 | Twice the yield of 316 with chloride SCC resistance; offshore topsides |
| Super Duplex 2507 | S32750 | Solution annealed | 750 | 550 | 15 | PREN > 40; seawater and desalination bolting |
| Titanium Grade 5 | R56400 | Annealed (ASTM B348) | 895 | 828 | 10 | Half the weight of steel, immune to seawater; aerospace and chemical |
| A-286 | S66286 | Solution treated + aged | — | — | — | Iron-base superalloy for 650 °C bolting; on request with certified values |
Bar minimums from the linked datasheets for the supply condition shown.
How Our Shoulder Bolts Are Made
1
Heading or turning
Small sizes are cold headed with the socket formed in the die; larger and special sizes are turned from bar and broached.
2
Undercuts & knurl
Relief groove under the head and thread undercut machined; head knurled where specified.
3
Thread rolling
The small thread rolled to 6g or 3A, concentric with the shoulder.
4
Heat treatment
Hardened and tempered to 39–44 HRC for 12.9 or HRC 32–43 for inch screws, in a controlled atmosphere.
5
Centreless grinding
Shoulder ground after hardening to f9 or the drawing tolerance, with a fine finish for smooth running.
6
Finish & inspection
Black oxide and oil or passivation, then shoulder diameter, length and runout checked.
Designing with Shoulder Bolts
Do
- Make the shoulder slightly longer than the moving part, for end play
- Give the base a flat, square face for the shoulder to seat on
- Tap the hole deeper than the thread so the shoulder seats before the thread bottoms
- Use a bronze or polymer bushing in the moving part for long wear
- Lock the thread with adhesive where vibration is present
Don't
- Clamp the moving part with the head: it will not turn
- Tighten to cap-screw torque: the thread or shoulder face will yield
- Load the thread in bending: carry side loads on the shoulder
- Mix up the ISO and commercial series (6.5 vs 6 mm shoulder)
Where Our Shoulder Bolts Are Used
Press tools & dies
Stripper bolts guiding spring-loaded stripper and pressure plates.
Linkages & pivots
Levers, clamps, toggle mechanisms and hinges in machines.
Rollers & pulleys
Axles for idler pulleys, cam followers, guide rollers and sprockets.
Automation & packaging
Grippers, indexers and stainless pivots on packaging lines.
Moulds & fixtures
Guides for floating plates, ejector systems and locating elements.
Vehicles & equipment
Pedal and linkage pivots, seat mechanisms and agricultural machinery.
Shoulder Bolt Inspection & Certification
| Check | Method | Applied to |
|---|---|---|
| Shoulder diameter | Micrometer or air gauge against f9 / drawing limits | Every lot, statistical sampling |
| Shoulder length | Height gauge from under-head face to shoulder face | Every lot |
| Runout & squareness | V-block and dial indicator; head-to-shoulder and shoulder-to-thread | Every lot |
| Thread | Ring gauges | Every lot |
| Socket | Go / no-go hexagon gauges | Every lot |
| Hardness | Rockwell C | Every heat-treatment lot |
Every lot ships with
- EN 10204 3.1 certificate with heat number
- Hardness results
- Shoulder diameter and length record
On request
- 100 % shoulder diameter inspection
- PPAP-style dimensional layout
- Third-party inspection
Shoulder Bolt Questions, Answered
A shoulder bolt, or shoulder screw, has a socket head, a precision-ground plain shoulder and a shorter thread of smaller diameter. When it is tightened, the shoulder face seats on the part and the shoulder stays free, so a lever, wheel, bushing or plate can turn or slide on it. Metric shoulder screws are made to ISO 7379 and inch ones to ASME B18.3. In press tools they are often called stripper bolts.
By shoulder diameter, thread and shoulder length, in that order. The length of a shoulder bolt is the length of the shoulder only, not counting the head or the thread. For example, 10 x M8 x 30 is a 10 mm shoulder with an M8 thread and a 30 mm long shoulder, and 1/4 x 10-24 x 7/8 is a 1/4 inch shoulder, 10-24 thread and 7/8 inch shoulder.
ISO 7379 pairs shoulders of 6.5, 8, 10, 13, 16, 20 and 25 mm with M5, M6, M8, M10, M12, M16 and M20 threads. Many catalogues use a commercial series with 6, 12 and 24 mm shoulders in place of 6.5, 13 and 25, plus 4 mm with M3 and 5 mm with M4. Inch shoulder screws use a thread one step smaller: 1/4 inch with 10-24, 5/16 with 1/4-20, 3/8 with 5/16-18, 1/2 with 3/8-16, 5/8 with 1/2-13 and 3/4 with 5/8-11.
Metric shoulders are ground to f9, which lies entirely below nominal: for a 10 mm shoulder that is minus 0.013 to minus 0.049 mm, and for a 16 mm shoulder minus 0.016 to minus 0.059 mm. ASME B18.3 inch shoulders are 0.002 to 0.004 inch under nominal, for example 0.2480 to 0.2460 inch for a 1/4 inch shoulder.
For a part that must turn or slide on the shoulder, an H7, H8 or H9 bore gives a clearance fit with an f9 shoulder. A 10 mm f9 shoulder in a 10 mm H8 bore has 0.013 to 0.071 mm clearance. Use the fit calculator on this page for other sizes, and make the shoulder slightly longer than the part so that the part is not clamped.
Tighten it enough to seat the shoulder face firmly on the part, not to the torque of a 12.9 socket head cap screw of the same thread. The shoulder face is a small bearing area and the thread is smaller than the shoulder, so standard-parts makers note that the tightening torque is limited by the shoulder, not by the property class. Use thread-locking adhesive where vibration could loosen the screw.
They are the same part. In press tools and dies a shoulder bolt holds the spring-loaded stripper plate: the plate slides on the ground shoulder and the head limits its travel, so toolmakers call it a stripper bolt. In machines it is used as a pivot, axle or guide for links, rollers and pulleys.
Metric shoulder screws are usually alloy steel in property class 12.9 with black oxide, or AISI 304 stainless steel. ASME B18.3 inch shoulder screws are alloy steel with 140,000 psi minimum tensile strength, 120,000 psi minimum yield and a hardness of Rockwell C32 to C43. We also make shoulder bolts in 316, 17-4PH, duplex and nickel alloys to drawing.