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Bolts · ASTM F3125/F3125M Grade F1852 and F2280

A4 (316) Stainless Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off)

Mechanical properties, corrosion behaviour and the full dimensional range for this grade.

A4 Stainless Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off) are supplied to ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80. Corrosion behaviour is superior, including marine and chloride environments, the material is largely non-magnetic, and the usable service range is approx. -200 °C to +400 °C, subject to the property class and the joint. In practice this grade is specified for marine, coastal and chemical applications.

Grade
ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80
Corrosion resistance
Superior, including marine and chloride environments
Magnetic response
Largely non-magnetic
Service temperature
approx. -200 °C to +400 °C, subject to the property class and the joint

Property values are typical for the grade. Certified mechanical test data is available on request for production orders.

A4 (316) Stainless Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off) reference image

A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. When tension-control structural bolt assemblies (tc / twist-off) are specified in this grade, the dimensions remain per ASTM F3125/F3125M Grade F1852 and F2280; the material determines corrosion behavior (superior, including marine and chloride environments) and the service temperature range (approx. -200 °C to +400 °C, subject to the property class and the joint). Both are covered below with the size table.

Why Choose A4 Stainless Steel for Tension-Control Structural Bolt Assemblies (TC / Twist-Off)

Specified for marine, coastal and chemical applications. For tension-control structural bolt assemblies (tc / twist-off), this matters when superior, including marine and chloride environments is the primary requirement.

Mechanical & Physical Properties

Grade designationISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80
Magnetic responseLargely non-magnetic
Service temperatureapprox. -200 °C to +400 °C, subject to the property class and the joint
Corrosion characteristicSuperior, including marine and chloride environments

Galvanic & Galling Considerations

Two important notes for stainless tension-control structural bolt assemblies (tc / twist-off): (1) stainless can gall on stainless threads under load — use a thread lubricant or anti-galling compound, especially for M6 and below; (2) when joined to aluminum or galvanized steel, stainless can drive galvanic corrosion of the less-noble metal in wet service — isolate with a coating or sleeve where appropriate.

Comparable Grades

For Tension-Control Structural Bolt Assemblies (TC / Twist-Off), the alternative stainless grade is A2 (304). A2 (304) suits general indoor and outdoor service; A4 (316) adds molybdenum for marine and chloride environments. Where higher strength matters more than corrosion, switch to plated alloy-steel class 8.8 or 10.9.

Using Stainless Fasteners in Aluminum

Stainless steel is more noble than aluminum, so in the presence of an electrolyte — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. The effect is driven by the area ratio: a small stainless fastener in a large aluminum section is normally acceptable, while a large stainless fastener in thin aluminum is not. Where the joint is wet, isolate the two metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.

Sizes of Tension-Control Structural Bolt Assemblies (TC / Twist-Off) Available in A4 Stainless Steel

SizeThread seriesAssemblyMinimum installation tension F1852 (lbf)Minimum installation tension F2280 (lbf)FinishReference standard
1/2-13UNCbolt + twist-off nut + washer12,55015,650Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
5/8-11UNCbolt + twist-off nut + washer19,90024,900Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
3/4-10UNCbolt + twist-off nut + washer29,45036,800Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
7/8-9UNCbolt + twist-off nut + washer40,75050,950Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
1-8UNCbolt + twist-off nut + washer53,45066,800Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
1-1/8-7UNCbolt + twist-off nut + washer67,35084,100Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
M16Metric optionbolt + twist-off nut + washerPlain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
M20Metric optionbolt + twist-off nut + washerPlain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280

Technical Drawing

Customize the parameters below — every spec field is editable, and the drawing redraws to match the values you choose. Changing the size will snap the other fields to that size's standard values; you can then override any individual value.

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Specification
Business Information

Dimensions & Specifications (ASTM F3125/F3125M Grade F1852 and F2280)

SizeThread seriesAssemblyMinimum installation tension F1852 (lbf)Minimum installation tension F2280 (lbf)FinishReference standard
1/2-13UNCbolt + twist-off nut + washer12,55015,650Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
5/8-11UNCbolt + twist-off nut + washer19,90024,900Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
3/4-10UNCbolt + twist-off nut + washer29,45036,800Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
7/8-9UNCbolt + twist-off nut + washer40,75050,950Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
1-8UNCbolt + twist-off nut + washer53,45066,800Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
1-1/8-7UNCbolt + twist-off nut + washer67,35084,100Plain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
M16Metric optionbolt + twist-off nut + washerPlain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280
M20Metric optionbolt + twist-off nut + washerPlain, heat-treated alloy steelASTM F3125/F3125M Grade F1852 and F2280

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

  • Industrial fabrication One-pass structural assembly where repeatable tension matters more than later disassembly.
  • Steel erection Matched structural bolt assemblies tensioned in beam, column and splice connections.
  • Bridge construction Slip-critical steel joints where the final tension is set by the twist-off installation system.
  • Heavy transport Truck frames and chassis joints exposed to road vibration and cyclic load.
  • Food, pharma & cleanroom Stainless assemblies that are washed down, where the finish matters as much as the strength.
  • 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

Inside the plant

Manufactured in our own plant

This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided.

  1. Wire rod feeding into a cold heading machine
    01

    Cold heading

    Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail.

    Head dimensions and under-head radius checked at set-up and per shift.

  2. Thread rolling machine producing bolt threads
    02

    Thread rolling

    Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch.

    Go / no-go ring gauges to ISO 965 tolerance class 6g.

  3. Baskets of bolts staged for heat treatment
    03

    Heat treatment

    Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it.

    Core hardness and tensile tested per lot to ISO 898-1.

  4. Zinc plated bolts in a treatment basket
    04

    Surface treatment

    Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list.

    Coating thickness and neutral salt spray hours to ISO 9227.

Frequently Asked Questions

Can A4 Stainless Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off) be used with aluminum?

Yes, but stainless drives mild galvanic corrosion of aluminum in wet service — isolate with a coating, sleeve or paint, or accept the trade-off if the joint is dry and indoor.

What's the service temperature limit for A4 Stainless Steel?

The practical service range is approx. -200 °C to +400 °C, subject to the property class and the joint.

Can A4 Stainless Steel replace plated alloy steel structurally?

Only at the standard strength classes — A2-70 / A4-80 are roughly equivalent to class 7 steel; A4-100 reaches class 8.8. For class 10.9 or 12.9 strength, plated alloy steel is required.

Are A4 Stainless Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off) magnetic?

A4 Stainless Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off) are largely non-magnetic.

How do I request a quotation?

Use the technical drawing on this page to pick the exact configuration, then submit it with the quote form. We respond within one business day.