Cap Nuts
What are cap nuts (acorn nuts)?
Cap nuts—often called acorn nuts—are hex nuts with a closed, domed end that covers the bolt or screw tip. The cap protects threads, improves safety by removing sharp exposed ends, and delivers a polished, finished look for decorative or cleanable assemblies.
Why choose cap nuts?
- Finished appearance – the domed top hides threads for a clean, professional look.
- Safety & protection – covers sharp ends and shields threads from dirt and damage.
- Simple assembly – installs like a standard hex nut with a wrench or socket.
- Material options – stainless and brass for corrosion resistance or aesthetics.
Types of cap nuts
- Standard Cap Nuts – general-purpose domed nuts for most finishing needs.
- High Crown Cap Nuts – taller dome for longer bolt projections.
- Extra Tall Cap Nuts – maximum thread coverage where longer studs are used.
Materials and finishes for cap nuts
- Stainless steel 18-8 / 304 – reliable corrosion resistance for most environments.
- Stainless steel 316 – enhanced resistance for coastal/marine or chloride exposure.
- Brass – decorative appearance with good corrosion resistance indoors.
- Nickel or zinc plated – bright finish on carbon steel for light indoor service.
Common applications for cap nuts
- Furniture, cabinetry, and architectural hardware
- Automotive, motorcycle, and bicycle finishing
- Fixtures, signage, guards, and covers where snag-free ends are important
- Food, medical, or clean spaces where smooth surfaces are preferred
How do I size and select cap nuts?
Match the nut to your bolt’s thread size and pitch (e.g., 1/4-20, 3/8-16, M8-1.25). Choose standard, high crown, or extra tall based on how far the bolt projects past the mating material—longer projections need a taller dome to fully enclose the tip. Select material/finish for the environment and appearance.
Installation tips for cap nuts
- Start by hand to avoid cross-threading. Tighten with a properly fitting wrench or socket.
- Do not bottom the bolt against the dome; leave sufficient clearance or choose a taller crown.
- For vibration, pair with a lock washer or use a jam nut against the cap nut.
- Match materials across bolt, washer, and nut to reduce galvanic corrosion outdoors.
Cap Nuts FAQs
Use the accordion below for quick answers about sizing, crown height, materials, and best practices for cap nuts.
They are the same fastener; “acorn nut” refers to the domed shape.
When the bolt projects farther past the joint and you need more internal clearance to fully cover the tip.
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Match the nut to your bolt’s diameter and thread pitch (e.g., 3/8-16 UNC, M6-1.0). If the bolt sticks out significantly, choose a taller crown.
Cap nuts are primarily for finishing and protection. For high-load or structural joints, follow the project spec for nut grade/class.
Yes, use 304 stainless for general outdoor exposure and 316 stainless for coastal/marine or chloride environments.
A flat washer can protect the surface and spread load; add a lock washer or a jam nut if vibration resistance is required.
Use a shorter bolt, choose a high crown/extra tall cap nut, or add a jam nut beneath the cap nut to set clamp load.
Brass is mainly chosen for appearance and corrosion resistance; use steel or stainless where higher strength is needed.
Yes, clean, etch/prime as appropriate for the base material; stainless often requires proper prep for coating adhesion.
Use the torque for the bolt size and grade, ensuring the bolt doesn’t bottom out in the dome. Stop if resistance increases abruptly.
They help by covering sharp ends and smoothing the surface, which is why they’re common on guards, furniture, and hand-contact areas.