Ordering the wrong size wire thread insert is one of the most common — and most avoidable — delays in a thread repair job. It usually happens the same way: a technician measures the damaged hole’s nominal size, orders an insert to match, and only discovers during installation that the drill and tap size required for that insert doesn’t match what was actually prepped. Getting the sizing sequence right the first time saves a second order and a second delay.
The key thing to understand is that a wire thread insert repair isn’t a direct size-for-size swap. Repairing a stripped thread means drilling out the damaged hole to a specific oversized diameter, then tapping it with a matching STI (screw thread insert) tap — not the standard tap that would have been used to cut the original thread. Only once that oversized, correctly tapped hole exists does the insert itself get installed. Skipping or guessing at this intermediate step is where most sizing errors happen.
This is why referencing a proper HeliCoil drill size chart before starting the job matters more than eyeballing it based on the original bolt size. The chart maps the original thread size directly to the correct drill diameter and STI tap required — removing the guesswork and preventing a mismatched order. Dimensional standards such as ASME B18.29.2M underpin these size charts, ensuring the relationship between original thread size, drill diameter, and insert size stays consistent regardless of manufacturer.
For technicians working across a wide range of legacy equipment where the original fastener specification isn’t always clearly marked or documented, a part number cross-reference tool can help confirm exactly which insert size and part number matches an existing or damaged component — useful when working from an old drawing or a part with worn or illegible markings.
It’s also worth checking sizing carefully when a hole has already been repaired once before. A hole that’s had a previous insert removed and is being repaired again may need to step up to an oversized insert variant rather than the standard size, since the original hole diameter has already been enlarged once. Our HeliCoil troubleshooting resource covers this and other common repeat-repair scenarios in more detail, including how to tell whether a hole has reached the point where a standard oversized insert is no longer sufficient.
Once the correct size is confirmed, ordering becomes straightforward — Thor stocks the full HeliCoil thread insert range across common and less-common sizes, with same-day or next-day availability on most standard sizes for Singapore-based buyers.
This small step matters most on jobs where the technician isn’t the one who will be doing the actual ordering — clearly documenting the confirmed drill, tap, and insert size before handing the job to procurement avoids the back-and-forth that often causes repair delays in larger organisations.
What to Do Next
Before placing an order for a thread repair, confirm the drill size, tap size, and insert size against a proper reference chart rather than working from memory or the original bolt’s nominal size alone. A five-minute check against the correct chart is considerably faster than waiting on a second, corrected order after an initial mismatch is discovered mid-repair.