Trojan Special Fasteners Ltd | Specialist Nuts Fasteners | Nuts Bolts Washers | Precision Polygon Turning | Fastener Manufacturer

Frequently Asked Questions (FAQs)

What is the difference between a dome nut and a cap nut?
Dome nuts and cap nuts are essentially the same product. "Dome nut" refers to the rounded dome shape, whilst "cap nut" describes its function of capping the thread end. Both terms are used interchangeably, along with "acorn nut" (due to its acorn-like appearance) and "crown nut". They all describe a hexagon nut with a closed, domed end.

What are the advantages of using dome nuts over standard hex nuts?
Dome nuts provide several key benefits: (1) Safety - covering sharp thread ends prevents injuries and snagging hazards; (2) Aesthetics - providing a clean, finished appearance for visible applications in automotive, furniture, and architectural work; (3) Thread protection - shielding threads from damage, contamination, dirt, and corrosion; (4) Weather resistance - preventing moisture ingress into threaded assemblies.

Can you manufacture dome nuts with flanges or collars?
Yes, we regularly manufacture flanged dome nuts to customer specifications. The flange or collar provides increased bearing surface area, distributing load more effectively and potentially eliminating the need for separate washers. This is particularly popular for automotive and furniture applications. Simply provide your drawing or detailed specification.

What is a prevailing torque dome nut?
A prevailing torque dome nut resists loosening from vibration without requiring additional locking compounds or split pins. There are two main types: (1) *Two-piece with nylon insert (DIN 986 - withdrawn standard, not manufactured by Trojan) where a plastic insert creates friction, and (2) Single-piece with mechanical deformation* (our speciality) where the nut body is deformed through side-crimping or top-deformation to create the locking effect. Our single-piece all-metal prevailing torque dome nuts offer superior temperature resistance (no 121°C limitation), better long-term durability, and consistent re-usable performance. We can manufacture to your specific torque specification and provide torque testing services.

What sizes of dome nuts can you manufacture?
We manufacture dome nuts in the following size ranges: Metric M3 to M52, Imperial 2BA to 2", and Unified #8 to 2¼". Both preferred standard sizes and non-preferred custom sizes are available. We also produce non-standard thread pitches (fine pitch, extra-fine, or custom) and special thread forms to specification.

What is the difference between high-crown and low-crown dome nuts?
High-crown (tall) dome nuts, manufactured to DIN 1587, have a more pronounced dome profile with greater internal depth, providing more thread coverage and a more substantial appearance. This prevents the bolt from touching the dome cap, ideal for vibration-prone applications. Low-crown (short or standard) dome nuts, manufactured to DIN 917, have a shallower dome profile, suitable where space is limited or a more subtle finish is required. SAE J483 defines both types for automotive applications.

Can you polish dome nuts for decorative applications?
Yes, we offer head polishing services on dome nuts, creating a mirror-like finish ideal for architectural, automotive, furniture, and high-end decorative applications where appearance is paramount. Polishing is available on stainless steel, brass, and chrome-plated carbon steel. We can achieve various finishes from satin to high-polish mirror finish.

What materials are best for outdoor or marine applications?
For outdoor applications, hot-dip galvanised carbon steel or grade 304 (A2) stainless steel dome nuts are suitable. For marine and coastal environments, we recommend 316 (A4) marine-grade stainless steel dome nuts with passivation treatment. Grade 316 offers superior corrosion resistance to salt water and chloride environments. Naval brass is also suitable for some marine decorative applications.

How do I specify a custom dome nut?
Provide us with either: (1) a technical drawing with dimensions including thread size, hexagon AF size, dome height, overall height, and material/finish requirements; (2) a sample part for reverse engineering; or (3) a detailed written specification. Our technical team will review your requirements and provide a quotation with lead time. We can also offer design suggestions to improve manufacturability if needed.

What delivery times can you achieve?
Lead times vary based on quantity, complexity, and material availability. Standard metric sizes (M6-M16) in carbon steel or 303/304 stainless may be available from stock or within 1-2 weeks for small batches. Custom specifications typically require 3-4 weeks for production quantities, with expedited service available for urgent requirements. Contact us with your specific needs for accurate delivery schedules.

Can you manufacture DIN 986 nylon insert dome nuts?
No, we do not manufacture DIN 986 two-piece dome nuts with nylon inserts. As a precision bar turning manufacturer, we specialise in single-piece dome nuts machined from solid bar stock. However, we can offer superior all-metal alternatives: single-piece prevailing torque dome nuts with mechanical deformation (side-crimped or top-deformed) that provide vibration resistance without nylon inserts. These offer higher temperature resistance (no 121°C limitation), better durability, and consistent re-usable locking performance. If you have a DIN 986 requirement, contact us to discuss suitable single-piece alternatives.