At some stage you may come across a thread that needs repair or a clean. Often previous use of thread locker will require a quick clean of the threads. If you leave previously hardened thread locker in the thread the you run the risk of damaging the thread, especially if it's in a soft material like aluminium.
What sizes?
For bicycles, three sized taps will come in handy:
- 4mm;
- 5mm; and
- 6mm.
You will also need a tap handle.
Tap and die set or individual?
You can buy these items separately, but it may work out cheaper to just buy a metric tap and die set. The other sizes may come in handy for other jobs around the house and the die can be useful for cleaning bolt threads.
Metric tap and die sets are fairly commonly available for around the $30 mark