Here is a list of Frequently Asked Questions about our line of thread repair inserts.  They are separated by insert type.

Coil type inserts 

Q1. What is the difference between Full-Torque thread repair inserts and coil type thread repair inserts?

A1. Coil type inserts are made of stainless steel wire whereas Full-Torque inserts are machined out of solid 1144 stress proof bar stock.

Q2. What are the disadvantages of coil type inserts?

A2. They can be difficult to install, they have a history of coming out, and they will only repair a stripped hole which means they cannot fix any other type of damage.

Q3. Why should I not use a coil type insert to fix a stripped spark plug hole?

A3. Stainless steel cannot transfer heat fast enough to allow the spark plug to properly cool. It is also very difficult to break off the installation tang during an in-frame repair.

Q4. Can I install a Full-Torque insert after a coil type repair has failed?

A4. Yes, the Full-Torque Thread repair inserts are larger in diameter than the coil inserts.

Q5. Can I fix a tapered pipe thread hole with a coil type insert?

A5. Coil type thread repair inserts have a difficult time sealing because it is impossible to seal completely around the coiled wire. Full-Torque inserts can seal up to 3,000 psi.

Q6. Can I stack coils on top of each other to repair a hole that is deeper than the coil?

A6. No this will not work and can cause the bolt to cross thread as it reaches the second coil. Full-Torque repair inserts come in long lengths to meet your application.

Q7. Where should I use Coil type inserts?

A7. Only in light duty applications where a hole is stripped or in soft metal like aluminum to help prevent the bolt hole from stripping.

Q8. What will happen if I install a coil type insert into a cracked bolt hole.

A8. The crack will spread when the bolt is tightened.  Installing a Full-Torque thread repair insert will draw the crack together as it is installed and will hold it together after the bolt is tightened.

Q9. Can I put a coil insert back in after it comes out.

A9. No, the installation tang was removed during the installation process.

Q10. What do I do if the installation tang doesn’t break off when I try to install the coil?

A10. The coil will need to be replaced. The first one is now unusable.

Key-locking inserts

Q1. If solid type thread repair inserts are better than coil type inserts, why do key-locking inserts strip out so often?

A1. Most key locking inserts are made of very soft steel and have an incomplete or shallow thread profile on the outside.

Q2. Can Key-locking inserts seal pressure tight?

A2. No, the key grooves extend over the full length of the insert and liquids and gasses can easily pass by.

Q3. What will happen if I install a key-locking insert into a cracked bolt hole?

A3. The crack will spread when the bolt is tightened into the inserts. Only a Full-Torque thread repair insert can pull the crack back together.

Q4. Why do the locking keys fail to keep the inserts from turning in aluminum?

A4. The keys do not extend outward far enough to get past the threads. The locking pins used to secure the Full-Torque inserts extend into the solid metal beyond the threads preventing rotation even in heated aluminum.

Q5. Can I stack the key locking inserts on top of each other to repair a deep hole.

A5. No, the keys need to be removed if the insert is installed below the surface so there is no way to keep it from turning and locking up on the bolt as the two inserts get out of time with each other. Full-Torque inserts are made long enough to meet your needs.

Q6. What is the advantage of having the internal threads lining up directly under the external threads?

A6. This is done to reduce the wall thickness of the insert to try to limit the loss of strength in the part being repaired. If the new drilled and tapped hole gets too close to an edge when installing any type of insert other than full torque insert, a crack can form from the bolt hole to the edge of the part. Only Full-Torque can add strength to the part.

Q7. Why does every size of key-locking insert require a different drill and special tap size?

A7. Because of the need to limit the wall thickness of the insert to reduce the loss of strength that occurs if heavy wall inserts with standard V style threads are used.

Only Full-Torque thread repair inserts uses the same drill and tap for several different internal size threads. Only 15 different tap sizes are used for all sizes ranging from ¼” or 6mm up to 2-3/8” or 60mm internal threads.

Q8. What can I do when a Key locking insert fails?

A8. Most often you will be able to use a standard Full-Torque thread insert. If a an oversized key-locking insert has been used to replace a failed thin wall key-locking insert, you can install a large Full-Torque FPS solid insert to fill in the hole.  After the hole is filled in you can drill and tap a new hole inside the FPS insert with what ever size threaded hole you want.

Q9. What do I do if I drill too deep when trying to install a key-locking insert and create a leak into the hole?

A9. You can install a Full-Torque FFB or FSB blind insert that has a solid bottom to prevent and seal leaks.

Q10. What do I do if I cannot find the exact insert that I need?

A10. You can install a stock FPS solid insert and simply drill and tap the hole size and   geometry that you need. Or, you can fill out the special insert request form found here and we can make them for you to your specifications.

Self tapping thread repair inserts;

Q1. What are the advantages of a self tapping thread repair insert?

A1. The only advantage is that you don’t have to tap the hole.

Q2. What are the disadvantages of self tapping repair inserts?

A2. Not using a tap to create the receiving hole for the new thread repair insert is similar to screwing a wood screw into a piece of wood. The thread cutting ability is very limited due to the shape of the flute and cutting edges of the insert so the threads are mostly formed much the same way the threads are rolled. This works fairly well in thin walls but has reduced ability to work in deeper holes. The biggest problem comes in attempting to install them into cast or ductile iron.  A severe spreading pressure is created when the insert is forced in that can easily crack the casting. Just like screwing a wood screw into wood too close to and edge will cause the wood to split.

Q3. What will keep the self tapping insert from coming out with the bolt the next time the bolt is removed?

A3. The self tapping inserts use capsulated thread locker as a retaining measure. The problem is that the thread cutting process strips the capsulated thread locker off the threads during installation. There is no clearance between the insert and the newly threaded hole for the thread locker.

Full torque permanent thread replacement

Q1. Where can I buy Full-Torque products?

A1. Direct from LOCK-N-STITCH Inc. or from a LOCK-N-STITCH distributor outside of the US. We manufacture everything in-house including the unique Spiralhook thread cutting taps. We ship worldwide and 98% of the time we can ship the same day if you call by noon Pacific Time unless you place an order for a special.

Q2. How do I know it will work where every thing else I have tried has failed.

A2. We guaranty it or we will refund 100% of cost including shipping. Hundreds of thousands of them have been installed in some of the most extreme conditions possible with no failures.

Q3. How many different inserts can I install with a single drill and tap which makes up most of the price for a kit?

A3. Here is an example; with an FT4 drill and tap you can install all of the following sizes in all the styles we make.

10 x 1.5mm, 11 x 1.5mm, 3/8-16, 3/8-24, 7/16-14, and 7/16-20

Q4. How much better will the bolt hole be after installing a Full-Torque insert?

A4. It will be stronger than the bolt or stud.

Q5. How close to an edge can I install a Full-Torque insert without weakening the part I want to repair?

A5. It doesn’t matter. The insert can actually even hang off the edge and the bolt hole will still be stronger than new.

Q6. What do I do if my bolt hole has a counterbore or non-threaded area above the threads?

A6. We manufacture many special inserts for special applications where counterbores are found such as head bolt holes and main bearing bolt holes in engine blocks. If we don’t have what you need on the shelf we can make it for you to match the original bolt hole. You can also order an FPS solid plug and make your own. Either way you will end up with the special Spiralhook threads that make all the difference in the world.

Q7. How well does Full-Torque work in soft metals like aluminum?

A7. Aluminum is very soft so any bolt hole that will receive even a few tightening and loosening cycles requires something harder for the threads to rotate against. It’s hard to measure the strength of a threaded hole beyond the strength of a grade 8 bolt with a tensile strength of 120,000 psi when they break before the insert fails.  If you need more than that we can harden the inserts to 40Rc which increases their strength to 180,000 psi which is the same as a grade 9 bolt. We believe that the bolt should fail before the insert.

Q8. Can I install spark plug inserts in an assembled engine without removing the heads?

A8. Yes, this is a common practice.

Q9. Where would I use an FST insert rather than an FFT style?

A9. The shoulder of the FST insert adds hoop strength around the bolt hole and provides a new flat surface around the hole that can fill in a chip or low spot.

Q10. How many inserts come in a kit?

A10. Each Kit contains 5 inserts with locking pins.

Q11. What else will I need if I want to install another size insert with a Full-Torque drill and tap that I already have?

A11. You will need to purchase the installation kit which includes a threaded stud a special hardened washer, a nut and drill bit and spacer tube for each size you want to install. These small kits are not very expensive.

Q12. Do I get more locking pins when I order replacement inserts?

Copyright © 2005 LOCK-N-STITCH