Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 800H Double End Studs
Double end studs are two-end-threaded stud bolts with a plain shank in the centre, used on through-flange and through-vessel bolting where both ends carry nuts and the plain centre passes through the bolt hole. TorqBolt machines Incoloy 800H double end studs from ASTM B408 round bar in diameter range M12 to M48 with overall lengths cut to flange standoff plus two-nut height plus chamfer allowance. The plain centre section is left unthreaded and finished to bar tolerance for clean through-hole fit. Both thread ends are machined to equal length, with end-chamfer for nut start. Every double end stud ships with EN 10204 type 3.1 mill test certificate covering heat traceability, ASTM B408 chemistry, solution-anneal cycle (1149 deg C plateau, rapid quench) and ASTM grain size 5 verification. Double end studs are the standard alternative to fully threaded stud bolts when the plain centre reduces thread-friction losses through long flange stacks on hot-zone service.
Double End Stud Dimensions (DIN 939 / ASME B18.2.1 Reference)
| Size designation | Across flats / OD | Head / nut height | Thread pitch | Standard reference |
|---|---|---|---|---|
| M12 | 12.0 mm OD | Each end: 1.25d (15 mm); Plain centre: balance | 1.75 mm | DIN 939 |
| M16 | 16.0 mm OD | Each end: 1.25d (20 mm); Plain centre: balance | 2.0 mm | DIN 939 |
| M20 | 20.0 mm OD | Each end: 1.25d (25 mm); Plain centre: balance | 2.5 mm | DIN 939 |
| M24 | 24.0 mm OD | Each end: 1.25d (30 mm); Plain centre: balance | 3.0 mm | DIN 939 |
| M30 | 30.0 mm OD | Each end: 1.25d (38 mm); Plain centre: balance | 3.5 mm | DIN 939 |
| M36 | 36.0 mm OD | Each end: 1.25d (45 mm); Plain centre: balance | 4.0 mm | DIN 939 |
| M42 | 42.0 mm OD | Each end: 1.25d (53 mm); Plain centre: balance | 4.5 mm | DIN 939 |
| M48 | 48.0 mm OD | Each end: 1.25d (60 mm); Plain centre: balance | 5.0 mm | DIN 939 |
Manufacturing Route at TorqBolt
Double end stud manufacture is a three-setup operation with controlled symmetry between the two thread ends and a precision plain centre:
- Receive Incoloy 800H bar to ASTM B408; PMI verification.
- Cut to overall length on bandsaw with square-end finish both ends.
- Centerless grind plain centre section to bar tolerance.
- Thread first end: length 1.25 to 1.5d, full depth, controlled chamfer.
- Reverse part in chuck; thread second end to equal length with controlled chamfer.
- Verify plain centre dimension and end-to-end symmetry on CMM.
- Solution anneal at 1149 deg C plateau followed by rapid quench; grain size 5 verified.
- Hardness band 120-184 HB; visual + dimensional + PMI inspection 100 percent.
- Heat-stamp grade marking; pack with VCI wrap and CoC + EN 10204 cert.
Double End Stud Sizes Stocked and Lead Times
| Diameter range | Length range | Stock status | Lead time |
|---|---|---|---|
| M12 - M24 | 75 mm - 400 mm | Made-to-order from stock bar | 10 to 14 working days |
| M27 - M36 | 100 mm - 500 mm | Made-to-order from stock bar | 14 to 18 working days |
| M42 - M48 | 150 mm - 600 mm | Made-to-order, large bar | 3 to 4 weeks |
| Above M48 | Per project drawing | Forged blank required | 5 to 7 weeks |
Inspection and Heat Marking
Specific double-end-stud inspections cover end-to-end symmetry, plain centre dimension and equal thread engagement:
- Both thread ends verified with the same ring + plug gauge set; thread lengths matched to print.
- Plain centre OD measured at three points along length and checked against bar tolerance.
- End-to-end symmetry checked: both threaded ends within 0.5 mm of design length.
- Hardness band 120-184 HB on first piece and one per batch.
- ASTM E112 grain-size etch verification showing grain size 5 or coarser.
- PMI by X-ray fluorescence on first piece and one per batch.
- Heat number stamped on one end for traceability.
- Visual inspection for thread damage, surface defects and chamfer integrity.
Typical Service Conditions
Double end studs are specified where the plain centre passes through a long flange-stack bolt hole and both ends carry nuts. Typical applications:
- Through-flange bolting on multi-flange stacks in heat exchanger tubesheets.
- Ethylene cracker radiant-section header bolting.
- ASME Section VIII pressure vessel through-flange joints.
- Reformer pigtail outlet header through-bolting.
- Steam superheater tube-bank header bolting on waste-heat boilers.
- Long-stack expansion-joint bolting on combustion-air ductwork.
Incoloy 800H Alloy Considerations on This Fastener Form
Companion Fasteners and Related Pages
- Stud Bolts: fully threaded version with no plain centre.
- Tap End Studs: one end short-thread, one end full-thread variant.
- Heavy Hex Nuts: matched nuts for both ends.
- Hex Nuts: lighter nut variant for less-critical service.
- Threaded Rod: continuous-thread alternative for field cut-to-length.
Frequently Asked Questions
Q. Why use a double end stud instead of a fully threaded stud?
The plain centre reduces thread-friction losses through long bolt holes and improves alignment on multi-flange stacks. The threaded ends carry the clamping load while the plain centre carries the bolt hole pass-through.
Q. What is the standard thread length on each end?
DIN 939 specifies 1.25d minimum thread engagement on each end. TorqBolt machines 1.25 to 1.5d default; deeper engagement is supplied on PO call-out.
Q. Can double end studs be supplied with unequal thread lengths?
Yes on call-out. Standard supply is symmetric (equal thread lengths both ends). Asymmetric configurations are machined to print on PO call-out.
Q. Is the plain centre size-on-size with the thread root or the thread OD?
Standard supply is plain centre to bar OD (size-on-size with thread OD). Reduced-shank variants with plain centre to thread-root diameter are supplied on PO call-out.
Q. Are double end studs available with both metric and inch thread combinations?
Yes on call-out. Default supply is matched metric or matched inch. Mixed-thread (metric one end, inch the other) is rare and machined to print on special order.
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