What is a special fastener?
A special fastener is a bolt, stud, nut, screw or machined component made to a drawing, sample or specification, rather than bought from a standard range. It is used when the size, thread, material, strength or paperwork needed is not available off the shelf, often in safety-critical work. HAGUE FASTENERS LIMITED has made special fasteners in the UK since 1971.
When do you need a special fastener?
Most fasteners are bought from stock to a standard such as ISO, DIN or ASME. A special is needed when a standard part will not do the job. The usual reasons are:
- Size or shape: a length, diameter, head or thread form that no stockist carries
- Material: a grade chosen for heat, cold, seawater or chemicals, such as Inconel 718 or super duplex
- Strength: a higher tensile class or a property a standard grade cannot reach
- Paperwork: traceable mill certificates, inspection and test plans, or nuclear QC1 release
- Replacement: a part for older plant where the original drawing or supplier no longer exists
- Quantity: one off or a small batch, which a high-volume maker will not run
Common types of special fastener
- Special bolts with non-standard heads, lengths or threads
- Studbolts and waisted turbine studs
- Heavy hex nuts and special nuts
- U-bolts, bent bolts, hook bolts and anchor bolts
- Socket screws, pins, plugs and precision turned or milled parts
Matching the material to the duty
| Service condition | Typical grades | What they bring |
|---|---|---|
| High temperature | B16, Durehete 1055, A453 660, Nimonic 80A, Inconel 718 | Strength and resistance to relaxation when hot |
| Low temperature | L7, B8, B8M | Impact toughness at low temperature |
| Seawater and subsea | Super duplex S32750 and S32760, Inconel 625, Monel K500 | Resistance to pitting and crevice corrosion |
| Chemical process | Hastelloy C276 and C22, Incoloy 825, Carpenter 20 | Resistance to aggressive acids and chlorides |
| High strength | Class 12.9 and 14.9, 17-4PH, Inconel 718, MP35N | High tensile strength in a compact joint |
| Non-magnetic or isolating | Austenitic stainless, bronzes, nylon, PTFE | Low magnetic response or electrical isolation |
These are typical choices only. The grade supplied always follows your specification. For more detail, see our guide to materials for specialist nuts and bolts.
How special fasteners are made
- Enquiry: you send a drawing, sample or description and we quote, often with options on material or route.
- Review: drawings, specifications and inspection plans are checked before the order is accepted.
- Material: certified, traceable bar from stock or approved UK, EU and US mills.
- Make: CNC turning, mill-turn and milling, with cut or rolled threads to ISO, ASME, BS and DIN.
- Inspect and test: calibrated inspection, PMI where specified, and UKAS-accredited testing.
- Release: parts are marked, certified, packed and delivered with your documentation.
Where special fasteners are used
Nuclear, defence, oil and gas, power generation, renewables, chemicals, shipbuilding, water, mining, construction and transport. In these industries a failed joint can stop a plant or put people at risk, so the material and the paperwork matter as much as the dimensions.
Frequently asked questions
What is the difference between a standard and a special fastener?
A standard fastener is made to a published standard and held in stock. A special is made to order for one application, to your drawing or specification.
Can you make just one?
Yes. HAGUE FASTENERS makes from 1 off, for prototypes and breakdowns, up to batches of several hundred.
Can you copy a part without a drawing?
Yes. We can work from a sample or a sketch and produce a drawing for your approval.
What certificates come with special fasteners?
Mill certificates with heat numbers carried through to release as standard, plus test reports, PMI, inspection and test plans or nuclear QC1 release where specified.
Need a special fastener?
Send your drawing, sample or specification to sales@haguefasteners.co.uk or call 01902 365865. See also: Special fasteners, Special bolts, Studs and Inconel fasteners.
