ASTM F3125/F3125M specifies the dimensions and tolerances for tension-control structural bolt assemblies (tc / twist-off). The full dimensional table is reproduced below, followed by the DIN, ISO and ASME parts that match or supersede it.
- Standard
- ASTM F3125/F3125M
- Product
- Tension-Control Structural Bolt Assemblies (TC / Twist-Off)
- Governing standards
- ASTM F3125/F3125M Grade F1852 and F2280
Equivalence between national standards is dimensional, not always metallurgical. Check the property class separately when substituting.
Tension-Control Structural Bolt Assemblies (TC / Twist-Off) manufactured to ASTM F3125/F3125M are dimensioned by the size table reproduced on this page. The standard fixes geometry and tolerances only; material and property class are assigned by ISO 898-1/898-2, and surface finish by separate finish standards.
ASTM F3125/F3125M — Scope
ASTM F3125/F3125M specifies the dimensions and tolerances of tension-control structural bolt assemblies (tc / twist-off). Material, property class, surface finish and packaging are governed by separate documents in the same standards family (for example ISO 898-1 for the mechanical property classes of bolts and screws).
Tolerance & Product Grades
ASTM F3125/F3125M, alongside the related ASTM F3125/F3125M Grade F1852 and F2280 entries on this site, specifies product grades (typically A or B for fine work and C for general engineering) and tolerance classes for the controlling dimensions. Choose the grade against the precision your application requires.
Dimensions Specified by ASTM F3125/F3125M
| Size | Thread series | Assembly | Minimum installation tension F1852 (lbf) | Minimum installation tension F2280 (lbf) | Finish | Reference standard |
|---|
| 1/2-13 | UNC | bolt + twist-off nut + washer | 12,550 | 15,650 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 5/8-11 | UNC | bolt + twist-off nut + washer | 19,900 | 24,900 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 3/4-10 | UNC | bolt + twist-off nut + washer | 29,450 | 36,800 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 7/8-9 | UNC | bolt + twist-off nut + washer | 40,750 | 50,950 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 1-8 | UNC | bolt + twist-off nut + washer | 53,450 | 66,800 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 1-1/8-7 | UNC | bolt + twist-off nut + washer | 67,350 | 84,100 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| M16 | Metric option | bolt + twist-off nut + washer | | | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| M20 | Metric option | bolt + twist-off nut + washer | | | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Tension-Control Structural Bolt Assemblies (TC / Twist-Off) page. Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
When to Specify ASTM F3125/F3125M
Choose ASTM F3125/F3125M for international engineering work and OEM supply where ISO standards are the contractual reference. It is the default modern specification for tension-control structural bolt assemblies (tc / twist-off).
Applications & Industries
Tension-Control Structural Bolt Assemblies are bought for a small number of well-defined jobs. These are the ones we ship them for. Stocked from 1/2-13 to M20 (screw size).
Industries that specify Tension-Control Structural Bolt Assemblies
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Industrial fabrication
One-pass structural assembly where repeatable tension matters more than later disassembly.
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Steel erection
Matched structural bolt assemblies tensioned in beam, column and splice connections.
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Bridge construction
Slip-critical steel joints where the final tension is set by the twist-off installation system.
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Heavy transport
Truck frames and chassis joints exposed to road vibration and cyclic load.
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Food, pharma & cleanroom
Stainless assemblies that are washed down, where the finish matters as much as the strength.
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Machine building & OEM
The default fastener on production equipment: covers, brackets, motor mounts and sub-assemblies tightened to a specified torque.
Typical applications
- using the plain shank and heavy hex geometry for steel-to-steel joints
- installing a matched bolt, nut and washer assembly with a controlled twist-off spline
- setting structural tension without a separate torque reaction wrench on the nut
- selecting F1852 or F2280 together with the required installation tension
- joints where the property class is stated on the drawing
- clamping two machined faces to a calculated preload
Service conditions to specify against
- Marine and coastal
- Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- High load
- Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
- Torque and preload
- The joint is designed around bolt tension, so lubrication, coating and the friction coefficient all change the torque figure — state them together.
Where to use something else
- Do not reuse the twisted-off spline or substitute a generic torque value for the grade-specific installation method.
- Do not use a machine thread into unthreaded sheet or timber; use a tapping screw, rivet nut or insert made for that parent material.
Full application guide: where Tension-Control Structural Bolt Assemblies are used, how to specify them, and the cases they are wrong for
