Thread tapping is fairly useful if you found that your bolt is jarred loose and has damaged the bolt itself and the threading of whatever it is you are screwing your bolt in to.
Before beginning to tap a thread, one should first understand roughly how it works.
Generally, if you have a size 10 (aka M10) bolt that is all chewed up and so is your thread (in this example my car seat railing mount) a tap that will be required would be to the next step (i.e. M12 in my case) before you buy, check to ensure the bolt can fit whatever you may need otherwise sleeving may be a good option for you (this is where the hole is tapped but a sleeve is installed to reduce the thread size to original).
What you need:
- A Tap of the size you need (in my case M12)
- A wrench that can fit the back of the tap (open ended)
- A battery powered hand drill with adjustable speed/tightness (only if you are experienced)
First tapper aka tap 1 is in the middle(which is on the carpet now)
tap 1 has a rather tapered angle to it. the reason for this is to flatten or carve off any residual threads and carving in new threads
tap 2 is located in the far right. this is identifiable as the tap that has the lesser taper to it
tap 3 which is in the far left (the one missing) is the thickest for it generally has a minimal taper and is used generally for creating the new threads.
1. Clean off any metal shards with a cloth/rag
2. Use tap number 1 (the middle one) and jam it into the hole as straight as you can (this might be a challenge)
3. Using a wrench, slowly turn tap number 1 until it catches (at all times ensuring it is straight)
4. Once it catches, slowly exert force as it will feel tight when you are tightening.
5. Every ½ a turn you turn to tighten, turn back a ¼ turn to release the shards from collecting in the teeth (this can cause the tap to jam and break off)
6. Once you are a ¼ of the length of the tap in, remove the tap and reinsert tap 1 by hand and continue until it reaches ½ the length of the tap.
7. Once done, change to Tap 2 (the one on the right) and perform step 3 to 6 again.
8. When done, use Tap 3 (the one on the right) and perform step 3 to 6.
9. Test your new threads with the new bolt. If the bolt cannot enter all the way, continue step 3 to 6 with Tap 2 followed by Tap 3
Note: If you have done this before, you may perform steps 3 to 6 with a hand drill. Please ensure the speed is low, the tap is inserted properly by hand first and the tightness settings on your drill is set to 4 or less (start low)
the completed thread
Job’s done. New Bolt fitting in perfectly and tightly.