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 Castle Nuts
Incoloy 800H castle nuts (DIN 935 / DIN 937) are slotted hex nuts that retain a cotter pin through a cross-drilled hole in the bolt shank to prevent rotational loosening. The slotted crown carries 6 radial slots (8 slots on the heavy-pattern variant) sized to receive the cotter pin. TorqBolt machines castle nuts from Incoloy 800H ASTM B408 round bar in diameter range M12 to M48 with hex across-flats matching the standard DIN 934 hex nut schedule. Internal threads are tapped to class 6H per ISO 965 (metric) or class 2B per ASME B1.1 (inch). The crown-slot geometry allows the cotter pin to seat in one of 6 angular positions around the bolt axis, providing positive loose-prevention on safety-critical applications. Every castle nut ships with EN 10204 type 3.1 mill test certificate documenting heat number, ASTM B408 chemistry, solution-anneal cycle and ASTM grain size 5 verification. Castle nuts are the standard nut form on lifting hardware, safety-critical pin retention and rotating equipment where loose-prevention must be visually verifiable.
Castle Nut Dimensions (DIN 935)
| Size designation | Across flats / OD | Head / nut height | Thread pitch | Standard reference |
|---|---|---|---|---|
| M12 | 12.0 mm thread | A/F 19 mm; Nut height 15 mm (incl. crown) | 1.75 mm | DIN 935 |
| M16 | 16.0 mm thread | A/F 24 mm; Nut height 19 mm (incl. crown) | 2.0 mm | DIN 935 |
| M20 | 20.0 mm thread | A/F 30 mm; Nut height 22 mm (incl. crown) | 2.5 mm | DIN 935 |
| M24 | 24.0 mm thread | A/F 36 mm; Nut height 27 mm (incl. crown) | 3.0 mm | DIN 935 |
| M30 | 30.0 mm thread | A/F 46 mm; Nut height 33 mm (incl. crown) | 3.5 mm | DIN 935 |
| M36 | 36.0 mm thread | A/F 55 mm; Nut height 38 mm (incl. crown) | 4.0 mm | DIN 935 |
| M42 | 42.0 mm thread | A/F 65 mm; Nut height 46 mm (incl. crown) | 4.5 mm | DIN 935 |
| M48 | 48.0 mm thread | A/F 75 mm; Nut height 50 mm (incl. crown) | 5.0 mm | DIN 935 |
Manufacturing Route at TorqBolt
Castle nut manufacture extends the standard hex nut process with a crown-section milling step to produce the 6 radial slots:
- Receive Incoloy 800H bar to ASTM B408; PMI verification.
- Cut bar into nut-plus-crown-height slugs.
- CNC mill the 6-sided hex profile per DIN 935 across-flats.
- Drill the through-hole; tap the internal thread to class 6H per ISO 965.
- Mill 6 radial crown slots: slot width sized to cotter pin diameter; slot depth per DIN 935.
- Solution anneal at 1149 deg C plateau followed by rapid quench; ASTM grain size 5 verified.
- Hardness band 120-184 HB on first piece and one per batch.
- Visual + dimensional + PMI inspection 100 percent; thread plug gauge verification.
- Pack with matched cotter pins (split pins per DIN 94) on PO call-out; CoC + EN 10204 cert.
Castle Nut Sizes Stocked and Lead Times
| Diameter range | Length range | Stock status | Lead time |
|---|---|---|---|
| M12 - M20 | Per DIN 935 | Made-to-order from stock bar | 10 to 14 working days |
| M24 - M30 | Per DIN 935 | Made-to-order from stock bar | 14 to 21 working days |
| M36 - M42 | Per DIN 935 | Made-to-order, large bar | 3 to 5 weeks |
| M48 | Per DIN 935 | Made-to-order, large bar | 4 to 6 weeks |
Inspection and Heat Marking
Castle nut specific inspections cover slot geometry, slot symmetry, internal thread compliance and across-flats:
- Slot width verified to receive matched cotter pin diameter.
- Slot depth verified per DIN 935 schedule.
- Slot symmetry checked: 6 slots equally spaced at 60 degrees.
- Internal thread verified with class 6H plug gauge.
- Across-flats verified per DIN 935 schedule.
- Hardness band 120-184 HB on first piece and one per batch.
- ASTM E112 grain-size etch verification.
- Heat number traceable to bar; PMI on first piece and one per batch.
Typical Service Conditions
Castle nuts are specified on safety-critical assemblies where positive loose-prevention with a cotter pin is mandatory:
- Eye bolt retention on lifting and tie-down assemblies subject to vibration.
- Pressure-vessel davit-arm and lifting-bracket pin retention.
- Heat exchanger shell-cover hinge-pin retention.
- Reformer catalyst-tube davit-arm pin retention.
- Furnace component hinge-pin retention on access doors.
- Ethylene cracker burner-air register linkage pin retention.
Incoloy 800H Alloy Considerations on This Fastener Form
Companion Fasteners and Related Pages
- Hex Nuts: standard nut without cotter-pin retention.
- Lock Nuts: prevailing-torque alternative for loose-prevention.
- Heavy Hex Nuts: heavy-pattern alternative for high-load bolting.
- Eye Bolts: matched eye bolts for castle-nut lifting assemblies.
- Washers: spacer washers for castle-nut installation.
Frequently Asked Questions
Q. What cotter pin should be used with a castle nut?
DIN 94 / ISO 1234 standard split pin sized to the bolt-shank cross-hole diameter and protrusion length per DIN 94 schedule. The pin is bent at install to retain the nut and bolt shank. Pin material should be compatible with the parent alloy (Incoloy 800H castle nut should use Incoloy 800H or Inconel 600 pin).
Q. What is the difference between DIN 935 and DIN 937?
DIN 935 is the standard castle nut with full nut height. DIN 937 is the low-profile castle nut with reduced nut height for restricted-clearance applications. Both use the same crown-slot geometry.
Q. Can castle nuts be supplied in inch sizes?
Yes. ASME B18.2.2 castle nuts 1/4 inch through 1-1/2 inch are machined on PO call-out from B408 bar with class 2B UNC threads.
Q. Are castle nuts re-usable?
Yes, but the cotter pin is single-use. Each installation requires a new cotter pin bent to fresh angle. The castle nut itself can be re-installed multiple times provided the crown slots are not damaged.
Q. Does the bolt shank require pre-drilled cross-holes?
Yes. Castle-nut assemblies require a cross-drilled bolt shank to receive the cotter pin. Cross-drilling is performed on the bolt or stud per print, sized to match the cotter pin diameter and angular position to align with one of the 6 crown slots.
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