What a thread repair kit saves you from
The three part problem. A wire coil insert repair only works if the drill, the tap, and the insert are all matched to the same specification, and the tap is the one people get wrong. It has to be an STI tap, cut to a deliberately oversized dimension that receives the coil, not a standard tap in the nominal thread size. Order a standard 1/4-20 tap for a 1/4-20 insert repair and you will cut a hole the coil cannot enter, having already drilled the original thread away. A kit removes that decision: everything inside is dimensioned to work together, so you drill, tap, and install without cross-referencing anything.
What is in a kit
- Wire coil inserts in the specified thread size, typically 1.5D length
- An STI tap cut to the correct oversize for the insert
- An installation tool that drives the coil by its tang
- Sized as a set, so no cross-referencing between components
Sizes available
- Machine screw sizes including #2-56, #4-40, #4-48, #10-24, #10-32, and #12-24
- Fractional coarse including 1/4-20, 3/8-16, and 1/2-13
- Fractional fine including 1/4-28 and 1/2-20
- Kits are supplied with 1.5D length inserts as standard
Common applications
- Stripped threads in aluminum engine blocks, heads, and casings
- Automotive, motorcycle, and small engine repair
- Machine tool and equipment maintenance
- Field repair where carrying matched components matters
- Shops handling occasional repairs across several thread sizes
- Any repair where the alternative is scrapping the part
If you already have the tap and tool, buy Helicoil inserts on their own. For inserts that need more pull-out strength than a wire coil provides, see solid thread inserts for metal.
Related Categories
- Helicoil Inserts
- Thread Insert Installation Tools
- Thread Inserts for Metal
- Thread Inserts
- Fastener Kits
Thread Repair Kit FAQs
Do I need a drill bit as well?
Check the kit contents, since some include the drill and others assume you have it. The drill size is specified for the insert and is larger than the original thread, so confirm you have the correct size before starting rather than partway through.
How many inserts come in a kit?
It varies by kit and size. Economy kits typically include enough inserts for several repairs at that thread size, which is useful because a hole that stripped once often has neighbours in the same condition.
Can I buy just the inserts as refills?
Yes. Once you have the tap and tool for a given size, you only need inserts for subsequent repairs. Our Helicoil insert range covers a much wider size selection than the kits do.
What thread sizes should a shop stock?
The sizes you actually strip. In automotive work that tends to be #10-24, 1/4-20, 5/16-18, and 3/8-16, since those cover most accessory and bracket mounting. Spark plug and specialty sizes are usually bought as needed.
Will a kit repair any stripped hole?
Only if there is sound material around it. An insert needs a solid boss to anchor into, so a cracked casting, a wall drilled too thin, or a hole already opened well oversize gives the insert nothing to grip. Assess the boss before committing.
What is 1.5D and is it enough?
1.5D means the insert is one and a half times the thread diameter in length, which is standard for general repair. For soft parent material like aluminum or higher load joints, a 2D insert gives more engagement, available separately in our Helicoil range.