Thread Inserts for Metal

What are thread inserts for metal? These are solid bushing inserts, machined from stainless bar with an external thread on the outside and a standard thread on the inside. Unlike a coiled wire insert, a solid insert is a rigid sleeve, which gives it substantially higher pull-out and torque-out strength and lets it survive repeated assembly and disassembly without wearing. The tradeoff is that it needs a larger hole, so more parent material is removed. AlbanyCountyFasteners.com stocks solid thread inserts in 303 stainless, in inch sizes from #4-40 through 3/4-10 and metric from M5 through M10.

Thread Inserts for Metal

When is a solid insert better than a wire coil?

Three situations justify the extra material removal. First, high load or high torque joints, where a solid bushing's greater wall section resists pull-out and torque-out far better than a wound coil. Second, assemblies that come apart repeatedly, since every disassembly cycle wears a thread, and a solid insert has more material to give. Third, anywhere the insert itself must resist rotating in the parent material, because a solid insert's external thread grips more positively than a coil's spring tension. If none of those apply and the boss is thin, a wire insert is lighter on material and cheaper. The question is not which is better in the abstract, but whether you have enough parent material to afford the larger hole.

Why choose solid thread inserts

Higher pull-out and torque-out strength than wire coil inserts
Better suited to repeated assembly and disassembly cycles
Rigid sleeve resists rotating in the parent material under load
Installs with a standard tap sized to the insert's external thread
303 stainless gives corrosion resistance and a clean machined thread

Sizes stocked

Inch coarse including #4-40, #6-32, #10-24, 1/4-20, 5/16-18, 3/8-16, and 3/4-10
Inch fine including #10-32, 1/4-28, 5/16-24, and 1/2-20
Metric including M5, M6, M8, and M10
Some sizes offered as metric to inch conversion inserts, which change the thread system

Common applications

High load threaded connections in aluminum and soft metals
Assemblies serviced and reassembled regularly
Machine tooling, fixtures, and jigs
Automotive and equipment repair where wire inserts are not enough
Converting a hole between metric and inch thread systems
Reinforcing new designs in soft material before threads fail

For general repair with minimal material removal, Helicoil wire inserts handle most jobs at lower cost. For wood rather than metal, see our thread inserts for wood.

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Thread Inserts for Metal FAQs

Do solid inserts need an STI tap?

No, and this is a practical advantage over wire coils. A solid insert is tapped with a standard tap sized to its external thread, so you do not need special STI tooling. Check the specified tap size for your insert before drilling.

How much stronger are solid inserts?

Noticeably higher in pull-out and torque-out strength, since a machined bushing has more material and grips through a positive external thread rather than spring tension. Exact figures vary by size and insert design, so check published values for critical joints.

Do they need more material around the hole?

Yes, that is the main tradeoff. A solid insert requires a larger tapped hole than a wire coil in the same nominal thread, so more parent material is removed. In a thin boss, that can leave too little wall, which is when a wire insert is the better choice.

Can these convert a thread between metric and inch?

Some sizes are made for exactly this, with a metric external thread and an inch internal thread or the reverse. It is a clean way to adapt a hole to different hardware without redesigning the part.

Are they removable?

Some solid inserts can be backed out with the right tooling, unlike wire coils which are generally permanent. Whether removal is practical depends on the insert type and whether any thread locker was used at installation.

What is 303 stainless?

A free-machining austenitic stainless, similar to 304 with sulfur added for cleaner machining. That machinability is why it is common in precision turned parts like solid inserts, and corrosion resistance remains good for typical service.