303 Stainless Steel Thread Inserts for Metal

Why 303 stainless for a solid insert?

Because these parts are machined, not formed, and machinability determines whether the thread comes out clean. 303 has sulfur added specifically to break chips during cutting, which produces sharper thread crests and better surface finish on a small turned part than a gummier grade like 304 would. On an insert, thread quality is the whole product: a ragged internal thread galls against the bolt and a ragged external thread does not seat properly in the tapped hole. You give up a small amount of corrosion resistance for it, since those sulfur inclusions are minor initiation points, but for an insert buried inside a hole that trade favors machinability every time.

Why choose 303 stainless solid inserts

• Higher pull-out and torque-out strength than a wire coil of the same thread
• Clean machined threads inside and out for smooth engagement
• Withstands repeated assembly and disassembly cycles
• Installs with a standard tap, no STI tooling required
• Corrosion resistance suitable for most indoor and general service

Inch sizes stocked

• Coarse including #4-40, #6-32, #10-24, 1/4-20, 5/16-18, 3/8-16, and 3/4-10
• Fine including #10-32, 1/4-28, 5/16-24, and 1/2-20
• Insert lengths vary with size, from around 0.250 inch on #4-40 up to 0.781 inch on 3/4-10
• Check the specified tap size for the external thread before drilling

Common applications

• High load threaded joints in aluminum housings and castings
• Machine tooling, jigs, and fixtures serviced regularly
• Equipment maintenance where wire inserts have failed before
• Reinforcing threads in new soft metal designs
• Precision assemblies needing consistent thread quality
• Any joint disassembled often enough to wear a tapped hole

For metric threads, see our metric 303 stainless thread inserts. Where the boss is too thin for the larger hole a solid insert needs, Helicoil wire inserts remove far less material.

Related Categories

• Thread Inserts for Metal
• Metric 303 Stainless Thread Inserts
• Helicoil Inserts
• Thread Insert Installation Tools
• Stainless Steel Thread Inserts

303 Stainless Thread Insert FAQs

What tap do I need?

A standard tap sized to the insert's external thread, not an STI tap. Each insert specifies its tap size, which is larger than the internal thread it provides. Drill and tap to that specification before installing.

How do I install a solid insert?

Drill and tap the hole to the insert's external thread size, then thread the insert in until it sits flush or slightly below the surface. Some designs use a driver tool, others accept a bolt and jam nut as an improvised driver. Thread locker can be used where rotation is a concern.

Are these stronger than Helicoil inserts?

In pull-out and torque-out, yes. The rigid sleeve and positive external thread grip better than a coil's spring tension. The parent material still sets the ultimate limit, so a strong insert in a weak boss does not deliver its full rating.

Will a standard bolt fit the internal thread?

Yes, the internal thread is a standard inch thread in the size listed. That is the point of the insert: the hole ends up accepting normal hardware regardless of what happened to the original thread.

Is 303 magnetic?

Nominally non-magnetic as an austenitic grade, though machining and cold work can induce a slight response. A magnet showing some attraction does not mean the part is not 303.

Can I use these outdoors?

Yes for general exterior service. In heavy salt or chloride exposure, the sulfur inclusions in 303 make it slightly less corrosion resistant than 304 or 316, so discuss the application with us if the environment is severe.