Standard Cap Nuts
What are Standard Cap Nuts?
Standard cap nuts—also called standard dome or acorn nuts—are hex nuts with a closed, domed end that covers the bolt or screw tip. They finish a joint neatly, protect exposed threads, and remove sharp edges in low-to-moderate torque applications.
Why choose Standard Cap Nuts?
- Clean, finished look – the dome hides threads for a polished appearance.
- Safety & protection – shields users and prevents thread damage or debris intrusion.
- Simple installation – tightens with a standard wrench or socket.
- Value – lower profile and cost than high crown or extra-tall versions when less thread coverage is needed.
Materials & finishes
- 304 / 18-8 Stainless Steel – dependable corrosion resistance for most outdoor uses.
- 316 Stainless Steel – higher resistance for coastal/marine and chloride exposure.
- Brass – decorative look with good indoor corrosion resistance.
- Zinc or Nickel Plated Steel – bright finish on carbon steel for light indoor environments.
Common uses for Standard Cap Nuts
- Furniture, cabinetry, signage, and architectural trim
- Automotive, motorcycle, and bicycle finishing hardware
- Guards, covers, and hand-contact areas where snag-free ends help
- Fixtures and displays requiring a smooth, clean surface
How to size and select Standard Cap Nuts
Match the nut to your bolt or screw diameter and pitch (e.g., 1/4-20 UNC, 3/8-16 UNC, M6-1.0, M8-1.25). Standard cap nuts suit short projections past the joint. If the stud extends farther and bottoms out in the dome, step up to a high crown or extra-tall cap nut. Select material/finish for the service environment and desired appearance.
Installation tips for Standard Cap Nuts
- Start threads by hand to avoid cross-threading; tighten with a properly fitting wrench or socket.
- Ensure the bolt doesn’t bottom out inside the dome; choose a taller crown if more clearance is needed.
- For vibration resistance, pair with a lock washer or jam nut beneath the cap nut.
- Match materials across bolt, washer, and nut to reduce galvanic corrosion outdoors.
Standard Cap Nuts FAQs
Use the accordion below for quick answers about sizing, crown height, materials, and best practices for standard dome cap nuts.
Standard has the lowest dome and least internal clearance; high crown and extra-tall provide more room to cover longer stud projections.
Match the nut to your bolt’s nominal size and thread pitch (e.g., 3/8-16, M8-1.25). If the stud hits the inside of the dome before the joint is tight, select a taller crown or shorten the bolt.
Yes, use 304 stainless for general outdoor exposure and 316 stainless for coastal or chloride-rich environments.
They’re primarily for finishing and protection. For high-load or structural connections, follow the specified nut grade/class for the joint.
A flat washer helps protect finished surfaces and spread load. Add a lock washer or a jam nut for vibration resistance when required.
Yes, as long as the stud projection is short enough not to bottom in the dome. For longer projections, use high crown/extra-tall.
Brass provides a warm decorative look; nickel-plated steel offers a bright finish; stainless gives a modern, clean aesthetic.
Generally yes, if threads are undamaged and the dome hasn’t bottomed during previous use. Replace if threads show wear or the dome is deformed.
Use the torque value for the bolt size/grade and lubrication condition. Stop if you feel the stud bottom in the dome.
They help by covering sharp ends and smoothing the surface, useful on handrails, guards, furniture, and similar applications.