Our grade 10.9 high-strength twist-off bolts (torsion shear / S10t type) are pre-assembled bolt-nut-washer connections engineered for steel structure and bridge projects where controlled pretension is a must.Backed by quench-and-temper heat treatment, batch-traceable material certificates and options from plain / black-oxide to hot-dip galvanized, our 10.9 twist-off bolts help you tighten faster, inspect quicker, and meet GB/T 3632 & ASTM F3125 on schedule.
Specification of High-Strength Twist-Off Bolts Grade 10.9
| Item | Specification / Option |
|---|---|
| Product type | High-strength twist-off (torsion shear) bolts - pre-assembled bolt + nut + washer |
| Grade | 10.9 standard; 8.8, 12.9 on request |
| Material | Alloy structural steel, quenched & tempered. Metric 10.9S (GB/T 3632): 20MnTiB, ML20MnTiB, 35VB, 35CrMo, 40Cr. Inch (ASTM F3125 / F1852 / F2280): Type 1 alloy steel, Type 3 weathering steel. |
| Standard | GB/T 3632 · GB/T 1228 · ASTM F3125 · ASTM F1852 / F2280 |
| Size (metric) | M16, M20, M22, M24, M27, M30 |
| Size (inch) | 5/8", 3/4", 7/8", 1" (on request) |
| Thread | Full / half thread; metric coarse or UNC/UNF per spec |
| Surface | Plain · Black oxide · Hot-dip galvanized (HDG) · others on request |
| Mechanical | Tensile ≤1000 MPa, yield ≤900 MPa; hardness, wedge-load and pretension per standard |
| Application | Steel frame, steel bridge, plant steelwork, tower & mast, large-span roof |
| Assembly set | 1 bolt + 1 nut + 1 washer (plain or galvanized per connection) |
| Documents | MTC, test report, warranty of conforming to GB/T / ASTM |
| Packaging | Carton + pallet; anti-rust inner layer for HDG |
| Lead time | 10–25 working days |
Why Choose Grade 10.9 Twist-Off Bolts?
Guaranteed, verifiable preload
The twist-off spline breaks off the instant the design pretension is reached, so the clamping force is controlled by the fastener itself, not by a torque wrench or operator judgement. A single visual check of the broken spline confirms the joint is correct - preload is consistent and repeatable, missed bolts are immediately visible, and no match-marking or wrench-angle checks are needed.
01
Faster, cheaper to install
Because tensioning is self-indicating, one operator on one side of the joint produces a correct bolted connection in seconds - ideal for towers, box columns and confined or at-height access. Fewer steps, less re-work and lighter tooling translate directly into a shorter, lower-cost erection programme.
02
Structural-grade strength
Grade 10.9 provides 1000 MPa nominal tensile and 900 MPa yield strength - the class structural engineers commonly rely on for load-bearing connections. Quench-and-temper heat treatment keeps hardness even across the section for dependable load transfer under shear, tension and dynamic loading.
03
Corrosion options for every duty
Match the finish to the environment and required service life - plain / black oxide for indoor shop-primed steelwork, hot-dip galvanized (salt-spray and coating-thickness validated, GB/T 13912 / ASTM A153) or weathering steel for coastal and outdoor projects.
04
Traceable factory quality
Every lot is tied to heat-treatment and test records by numbered batches, with material certificates (MTC) and test reports prepared with the goods - built to GB/T 3632 & ASTM F3125 and supplied as ready-to-use bolt + nut + washer kits, with wrench and technical guidance available.
05
Standards & Bolt Tension (10.9 Grade)
| Size | Pitch (mm) | Design Pretension (kN) | Min. Tensile Load (kN) |
|---|---|---|---|
| M16 | 2.0 | 100 | 163 |
| M20 | 2.5 | 155 | 255 |
| M22 | 2.5 | 190 | 315 |
| M24 | 3.0 | 225 | 376 |
| M27 | 3.0 | 290 | 477 |
| M30 | 3.5 | 355 | 583 |
| Referencing GB/T 3632-2008 and JGJ 82 pre-tensioning design tables; full test curves, MTC and third-party test reports on request. | |||
Principal Dimensions (metric)
Big-hexagon high-strength bolt head; bolt length L & thread length selected per the connection drawing.
| Size d | Pitch p (mm) | Head width s (mm) | Head height k (mm) | Across-corner e (mm) | Thread |
|---|---|---|---|---|---|
| M16 | 2.0 | 27 | 10.0 | 30.2 | Full / half |
| M20 | 2.5 | 34 | 12.0 | 38.0 | Full / half |
| M22 | 2.5 | 36 | 13.5 | 40.3 | Full / half |
| M24 | 3.0 | 41 | 14.5 | 45.9 | Full / half |
| M27 | 3.0 | 46 | 16.0 | 51.5 | Full / half |
| M30 | 3.5 | 50 | 18.5 | 56.0 | Full / half |
| Dimensions in mm, nominal, big-hexagon head per GB/T 1228 & connection per GB/T 3632 (e ≈ 1.12 × s). Bolt length L and thread length are finalised on the project drawing; inch sizes (5/8"–1") on request. | |||||
Surface & Finish
| Finish | Best For | Corrosion |
|---|---|---|
| Plain / Black oxide | Indoor steel structure, shop primer areas | Indoor |
| Hot-dip galvanized (HDG) | Outdoor bridges, roofs, transmission structures | High - meets ASTM A153 / GB/T 13912 |
| Alternative layers (Dacromet, etc.) | Coastal / high-humidity projects | On request |
Applications of Grade 10.9 Twist-Off Bolts
Plant & workshop steelworks
Frame joints, roof-truss chord splices and crane-girder end connections - dozens of identical bolts that must all hold the same preload.
01
High-rise steel buildings
Column-to-column splices and beam-column moment (rigid) connections, where guaranteed preload preserves frame stiffness and seismic safety.
02
Steel bridges & box girders
Main-girder field splices, cross-beam and diaphragm flange connections, and wind-bracing gusset joints.
03
Stadiums & long-span roofs
Space-frame tube nodes, large truss chord and web splices, and support node connections with a very high bolt count per joint.
04
Power-plant boiler steelwork
Boiler support frames, platform stringer-to-beam connections and heavy-equipment anchor joints under sustained load.
05
Transmission & telecom towers
Latticed angle members, leg splice plates and cross-arm joints - mostly bolted from one side while working at height.
06
Machinery & heavy-equipment bases
Anchor bolts and base-plate-to-foundation connections that carry vibration and dynamic in-service loading.
07
Railway & metro station steelwork
Concourse platform frames, waiting-hall canopies and long-span station roof connections needing repeatable, inspectable joints.
08
Retrofits & field repairs
Adding or replacing structural bolts in existing frames and trusses where quick, reliable tensioning must not interrupt service.
09
Warehouse & light-steel buildings
Portal-frame haunch joints, purlin-to-rafter and standard truss connections that profit from simple, fast twist-off installation.
10
Our Quality Control
Beyond routine diligence, we test the properties that matter most to a twist-off product - above all, that the spline breaks at the specified pretension. Each batch goes through:
| Test | Reference | What it verifies for twist-off bolts |
|---|---|---|
| Pretension / spline-break test | GB/T 3632 | The most critical check - confirms the spline snaps at the design pretension for each size. |
| Chemical composition (spectrometer) | GB/T 3077 / ASTM | Confirms the alloy-steel basis is correct before processing. |
| Hardness (HRC / HV) | GB/T 1231 / ASTM F606 | Confirms uniform quench & temper; rejects soft or uneven heat treatment. |
| Tensile / axial load | GB/T 3632 / ASTM F606 | Verifies min. tensile load of the finished bolt. |
| Wedge-load (head) test | ASTM F606 | Confirms head / shank integrity under eccentric load. |
| Impact test | GB/T 229 | Charpy toughness where a low-temperature or project specification requires it. |
| Thread gauge (GO / NO-GO) | GB/T 3934 | Ensures thread fit with the matching nut. |
| Decarburization / metallography | GB/T 224 | Checks surface decarb control - important for 10.9 delayed-fracture sensitivity. |
| Salt-spray & coating thickness (HDG) | GB/T 10125 / GB/T 6462 | Corrosion resistance and zinc-mass validation for galvanized orders. |
| Third-party re-inspection | e.g. SGS / TÜV | Optional independent verification on request. |
What Buyers Worry About - and How We Ensure It
| What you may be worried about | How we guarantee it |
|---|---|
| Bolts being missed or falsely reported on site? | The snapped spline is a visible "passed" mark - inspection is instant and cannot be faked. |
| Pretension not strong or even enough? | Each size is factory-tested so the spline breaks at the set design pretension (GB/T 3632). |
| Galvanized bolts holding up outdoors? | HDG is validated by salt-spray and coating-thickness tests meeting GB/T 13912 / ASTM A153. |
| Consistent quality across large batches? | Lot & batch numbers with MTC trace every delivery back to heat and test records. |
| Certificate delays at handover? | Commercial docs, MTC and test reports are prepared with the shipment; third-party reports on request. |
| Lead time for urgent projects? | Sample orders ship fast; production lead time is 10–25 working days. |
| Installation guidance or the right tooling? | Compatible torsion-shear wrenches and technical guidance are offered with the order. |
Packaging & Shipping
| Item | Detail |
|---|---|
| Seal | Bolt, nut, washer supplied per connection set; packing at customer's choice |
| Package | Carton & pallet (waterproof inner layer for HDG) |
| Lead time | 10-25 working days depending on size & quantity |
| MOQ | Small order accepted for sample / trial |
| Payment | T/T, L/C (negotiable) |
| Documents | Commercial invoice, packing list, MTC, test report |
FAQ:
What is a twist-off (torsion shear) bolt?
A pre-assembled bolt + nut + washer whose spline snaps off automatically at the set pretension, guaranteeing consistent clamping force.
Does hot-dip galvanizing affect the pretension or spline break?
No. Galvanized bolts are validated with the same spline-break pretension test together with salt spray and coating-thickness checks.
Can I get a twist-off shear wrench / driver together with the bolts?
Yes, we can bring or recommend a compatible electric shear wrench to match the connection set ordered.
Do you issue full certificates and test reports?
Each batch ships with material certificates (MTC); third-party test reports and test curves are provided on request.
How is on-site acceptance done?
Mainly by visual inspection - bolts whose spline is broken are compliant, so there is no need to re-check torque on every bolt as with the torque method.
