Metric 303 Stainless Steel Helicoil Inserts

Why metric inserts matter for imported equipment

Because the alternative is a bodged repair that fails twice. When an M8 thread strips in a European gearbox or a Japanese engine casing, the temptation is to drill it out and tap it to the nearest inch size, which works right up until someone needs the correct metric bolt to go back in, or until the next person servicing it finds a thread that matches nothing on the machine. A metric wire insert restores the hole to M8, keeps the original hardware usable, and leaves no surprise for whoever opens the assembly next. On anything built to metric drawings, matching the repair to the original specification is worth the extra effort of sourcing the right tap.

Why choose metric 303 stainless inserts

• Restores the hole to its original metric thread, so factory hardware still fits
• Free-machining 303 stainless gives a clean, hardened thread surface
• Corrosion resistance for engine, outdoor, and marine repairs
• Adds minimal wall thickness, suiting thin metric bosses
• Leaves no non-standard thread for the next person servicing the assembly

Sizes and specification

• Metric coarse threads including M6 and M14
• Lengths specified as a multiple of diameter, commonly 1.5D
• Requires a metric STI tap sized to the insert, not a standard metric tap
• Contact us if you need a metric size not listed

Common applications

• Imported machinery, European and Asian built equipment
• Metric engine blocks, cylinder heads, and gearbox casings
• Motorcycle and scooter repair on metric assemblies
• Industrial equipment built to metric drawings
• Bicycle frames, components, and metric threaded fittings
• Any repair where the original bolt must still fit afterward

For inch threads, see our 18-8 stainless Helicoil inserts. You will need a metric STI tap and driver from our installation tools.

Related Categories

• Helicoil Inserts
• 18-8 Stainless Helicoil Inserts
• Metric 303 Stainless Thread Inserts
• Thread Insert Installation Tools
• Thread Repair Kits

Metric Helicoil Insert FAQs

What is 303 stainless?

A free-machining austenitic stainless, close to 304 in composition with sulfur added to improve machinability. Corrosion resistance is very similar in normal service, and the improved machining characteristics are why it is common in precision made insert lines.

Can I use an inch insert in a metric hole?

No. The insert must match the thread you want to end up with, and the STI tap must match the insert. Mixing systems leaves you with a thread that accepts neither the original metric bolt nor a standard inch one.

Do I need a metric STI tap?

Yes. Like inch inserts, metric wire inserts require an STI tap cut to the oversize dimension for the insert, not a standard metric tap in the nominal size. Check the tap size specified for your insert before starting.

Is 303 as corrosion resistant as 304?

Slightly less, because the sulfur that improves machinability also creates small inclusions that can be corrosion initiation points. In practice, for a thread insert inside a hole, the difference rarely matters. For severe marine exposure, discuss the application with us.

What length should I choose?

1.5D suits general repair. Where the parent material is aluminum or the joint carries higher load, a longer insert spreads stress over more of the boss, so specify 2D if available in your size.

What if my metric size is not listed?

Contact us with the thread size and the depth of the hole. Metric wire inserts follow a standard progression and we can advise on availability for sizes outside the listed range.