How to Choose Aircraft Fasteners and Bearings for Maintenance

Small parts carry big loads on an aircraft. A wrong fastener or bearing can cause premature wear, joint failure or compliance problems during an audit. Here is what to check before you buy.

Know the Specification First

Most aircraft fasteners follow AN, MS, NAS or NASM standards. The part number tells you the material, size, head style and finish, so always match it to your illustrated parts catalog or maintenance manual rather than relying on a description. Parts are sometimes superseded, so confirm the current number before ordering.

When you source aviation hardware, check these details:

• Material: aluminum, alloy steel, corrosion-resistant steel or titanium. Never substitute without approved data.
• Grip length: the unthreaded portion should sit in the joint, not in the threads.
• Locking method: self-locking nuts, cotter pins or safety wire. Some locking nuts have reuse limits.
• Finish: plating protects against corrosion and must suit the surrounding structure.

Check Bearings Closely

Bearings in flight controls, landing gear and hinge points are chosen by type (plain, ball or roller), dimensions, load rating and seal style. Two bearings of the same size can have very different capacities, so verify the specification before ordering.

Ask for Traceability

Request a certificate of conformance and manufacturer traceability with every order. Look out for inconsistent markings, unusually low prices or suppliers who cannot name their source. Working with an AS9120B-accredited distributor adds process control, but you should still inspect parts on arrival.

Match Hardware With Larger Parts

If a repair also needs a replacement unit or assembly, browse aircraft components by part type so the hardware and components arrive together and match.

Quick Checklist

1. Confirm the part number against your manual.
2. Check for supersession or approved alternates.
3. Verify material, grip length and finish.
4. Request a CoC and traceability documents.
5. Inspect markings and packaging on arrival.

Frequently Asked Questions

What is the difference between AN and MS fasteners? AN is the older Army-Navy series. MS (Military Standard) covers many parts that replaced or updated AN designs. Dimensions can be similar, but always confirm the specified part in your manual.

Can I substitute a different fastener material? Not without approval. Changing the material affects strength, corrosion behavior and fatigue life, so any substitution must follow approved data.

Why does aviation hardware need traceability? Traceability links a part to its manufacturer and production lot. It lets problems be tracked and corrected, and it proves the part is genuine during audits.

Can aircraft locking nuts be reused? It depends on the nut type and the manufacturer’s limits. Check your maintenance manual and replace any nut that no longer holds its locking torque.

What documents should come with aircraft parts? At minimum, a certificate of conformance and manufacturer traceability. Structural fasteners may also need material and process certifications.

How do I spot a counterfeit fastener? Look for missing or inconsistent head markings, unusual plating or finish, prices far below market and vague traceability. Verify the supplier and inspect parts on arrival.