Thread Repair Kits Metric: Choosing the Right One
Four metric thread repair kits compared on sizes, insert counts, drills, taps, case and warranty, from a 131-piece set to a 332-piece set.
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When a bolt hole strips in an engine block or a bracket, thread repair kits metric are the fix: a metric kit drills the damaged hole oversize, taps a new thread and winds in a wire thread insert, and the bolt threads into the insert instead of the damaged metal. The kits in this guide all cover the common metric sizes, and they differ in piece count, insert counts, case and warranty. Pick the size range first, then check the insert counts for the sizes you use.
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Below: how a metric kit repairs a stripped thread, what the size numbers mean, what to check before buying, and the four kits in this guide.
OMT 172pc Thread Repair Kit Metric Restorer
A 172-piece metric thread repair kit with 5 drill bits, 5 taps, 150 wire thread inserts and 10 installation tools, with a 1 year warranty.
Pros
- 150 wire thread inserts, the only total insert count stated here
- Heat-treated HSS with a titanium coating
- States a 1 year warranty
- Blow-molded case holds every part
Cons
- No insert length is stated
- Metric sizes only, no SAE sizes in the listing
- No per-size drill bit dimensions are stated
- No weight is stated
CRAFTZONE 332PC SAE Metric Thread Repair Helicoil
A 332-piece thread repair kit covering metric M5 to M12 and SAE 1/4 to 1/2 with 304 stainless inserts and heat-treated HSS drills and taps.
Pros
- Covers metric M5 to M12 and SAE 1/4 to 1/2, the broadest range here
- 332 pieces, the largest kit here
- 304 stainless inserts, corrosion-resistant by the listing
- Lists 3.2 pounds, the only weight stated here
Cons
- No warranty term is stated
- No insert counts per size are stated
- No case dimensions are stated
- No insert length is stated
BILITOOLS Helicoil Thread Repair Kit Metric
A 131-piece metric thread repair kit covering M5 to M12 with 4241 HSS drills and taps and 304 stainless inserts in a blow molded case.
Pros
- Covers M5, M6, M8, M10 and M12 with 25 inserts each up to M10 and 10 of M12
- 4241 HSS drill bits and taps with a 135 degree apex angle
- 304 stainless inserts for longer lasting threads
- Blow molded case keeps every part organized
Cons
- No warranty term is stated
- Metric sizes only, no SAE sizes in the listing
- No case dimensions are stated
- No insert length is stated
Metric Helicoil Thread Repair Kit
A 131-piece metric thread repair kit with HSS drills, taps, heli coil inserts and chaser tools in a steel carrying case.
Pros
- Covers M5 to M12 for automotive and engine repairs
- HSS drills, taps, heli coil inserts and chaser tools in one kit
- Steel carrying case for transport and storage
- Title names spark plug and cylinder rethreading among its uses
Cons
- No warranty term is stated
- No insert counts per size are stated
- No weight is stated
- No insert length is stated
Thread repair kits metric: how a kit fixes a stripped thread
A stripped thread is a hole whose internal thread no longer grips the bolt. A metric thread repair kit restores it in stages, and every kit in this guide carries the tools for each one: a drill opens the damaged hole to a clean size, a tap cuts a new thread in the hole, and an insert winds into that new thread to give the bolt a fresh thread to grip. The insert stays in the hole, and the original bolt threads into it. The insert has a small tang for the installation tool, and a break-off tool snaps it off once the insert sits at depth, leaving a clean, ready-to-use thread.
The drill angle matters to the cut. The BILITOOLS listing states a 135 degree apex angle on its twist drills, claiming stronger metal penetration, and the OMT listing states 135 degree drill bits that quickly create space for the installation tools. A kit that states its drill angle and its insert material tells you more than one that lists only a piece count.
Metric sizes and what the numbers mean
Metric thread sizes read as a diameter and a pitch. The BILITOOLS listing spells it out: M5 x 0.8, M6 x 1.0, M8 x 1.25, M10 x 1.5 and M12 x 1.75. The first figure is the bolt diameter, and the second is the distance between threads. Match the kit to the bolt: a kit that covers M5 to M12 covers the common metric sizes in a home garage, and the CRAFTZONE kit adds SAE sizes from 1/4 to 1/2, with 3/8-16 called out as a common size.
Insert counts matter as much as sizes. The BILITOOLS kit lists 25 inserts each of M5, M6, M8 and M10, and 10 each of M12, while the OMT kit lists 150 wire thread inserts without a per-size count. The SEDY and CRAFTZONE listings state no insert counts at all, so their piece counts tell you the size of the box, not how many inserts of your size it holds.
What to check before you buy
Start with the size list. All four kits here cover M5, M6, M8, M10 and M12, so the metric range is the same across them, and the CRAFTZONE kit adds SAE sizes from 1/4 to 1/2. The choice turns on what comes with each kit: insert counts, drill and tap counts, case and warranty. The BILITOOLS kit lists 5 drill bits, 5 taps and 5 break pin tools; the OMT kit lists 5 drill bits, 5 taps and 10 installation and tang break-off tools. The SEDY and CRAFTZONE listings do not break out tool counts, so compare them on piece count and range instead.
Then check the case and the warranty. The BILITOOLS and OMT kits come in blow molded cases, the SEDY kit in a steel carrying case, and the CRAFTZONE kit in a molded storage case. Only the OMT listing states a warranty, 1 year, and the other three state no warranty term. Only the CRAFTZONE listing states a weight, 3.2 pounds, so the other three cannot be compared on weight. Torque matters once the insert is in: the BILITOOLS listing notes its inserts allow higher torque in weaker metals, and the 1/4 vs 3/8 torque wrench comparison covers the wrenches for small fasteners.
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Thread repair kits metric picks
These four kits handle the drilling, tapping and inserting above, from the 131-piece BILITOOLS set to the 332-piece CRAFTZONE set.
FAQ: garage tools
What sizes does a metric thread repair kit cover?
All four kits in this guide cover M5, M6, M8, M10 and M12. The CRAFTZONE kit also covers SAE sizes from 1/4 to 1/2, with 3/8-16 called out as a common size.
How many inserts come in a metric thread repair kit?
It varies by kit. The BILITOOLS kit lists 25 inserts each of M5, M6, M8 and M10, and 10 each of M12. The OMT kit lists 150 wire thread inserts without a per-size count, and the SEDY and CRAFTZONE listings state no insert counts.
Does a metric thread repair kit include a warranty?
Only one here does. The OMT listing states a 1 year warranty, and the BILITOOLS, SEDY and CRAFTZONE listings state no warranty term.
What is the difference between a 131-piece and a 332-piece kit?
Range and count. The 131-piece BILITOOLS and SEDY kits are metric only, covering M5 to M12, while the 332-piece CRAFTZONE kit covers metric M5 to M12 and SAE 1/4 to 1/2. Piece count alone does not say how many inserts of your size are inside.
Can I use a metric thread repair kit on a spark plug hole?
The listings name it among their uses. The SEDY title names spark plug and cylinder rethreading, and the CRAFTZONE listing calls itself a spark plug helicoil kit. Check the plug thread against the kit’s insert sizes first: the kits here list M10 x 1.5 and M12 x 1.75 inserts, so a plug thread in a different pitch does not match.
What does M8 x 1.25 mean?
It is a metric thread size from the BILITOOLS listing: M8 is the bolt diameter, and 1.25 is the thread pitch, the distance between threads.
Related: best thread repair kit and the 1/4 vs 3/8 torque wrench comparison.
