Recommend me a rethreading kit

Just buy the taps and dies you need as you need them and the relevant holders.

Inevitably you only ever use one or two and the rest of the set just goes unused. Then you break or lose the one you need so you end up replacing that and the rest continue to be unused.

Makes sense. Brands recommended, or to avoid?

I've got both US.Pro  metric and imperial tap and die sets (both the 40pc versions), haven't (touch wood) snapped one yet.  They were only about £26 each.

Counter to Josh's opinion, at least having the common sizes in a set means that when you f*** up, you have the tools to hand to fix it, not next weekend. And as long as you use at least 3 of them at some point you'll probably get your moneys worth.  If you do any DIY on your car they're great for cleaning out old rusty threads or taking the excessive paint out of the threads in new parts.

Now for the bad news, bike mech hangers are 10x1mm thread, which is neither of the standard M10 threads.  Pedal axles are 9/16, again not one you'll find in most sets, and one side is reversed.

What you've linked to is a thread repair tool.  Which is probably the correct tool for what you're asking for, it's designed to pull itself into an existing thread and straighten out the damaged metal.   Whereas a Tap is designed to cut away metal to create new threads.  You can use a tap to repair a thread, but it can also make a mess and cut out the wrong material and leave you with less thread than you  had to begin with. Likewise a thread repairing tap might not be sharp enough to cut into really excessive paint or a badly distorted thread.

Thanks, that also makes a lot of sense. Just remembered I've got a helicoil set - are the taps in that the same size as standard bike threads (eg bottle bosses at M5 x 0.8)?

Don't to go chewing anything up though so might take a punt on that set, assuming it's not going to be made of finest cheesium.

Buy a set rather than individual that you may need now. If you buy in bits you'll end up stuck for one, usually on a Friday, while at least having a range they're there for whatever pops up, be that bike or non bike related.

Make sure the ones you get are HSS at least. Those will last.

Thanks, that also makes a lot of sense. Just remembered I’ve got a helicoil set – are the taps in that the same size as standard bike threads (eg bottle bosses at M5 x 0.8)?

There might be, but probably not.  They use a scaled up version of the thread you are repairing.  e.g an 5 thread is 0.8mm pitch, so the helicoil tap probably looks like an M6, but will have a 0.8mm pitch not 1.0mm so that the coil sits in the threads.

assuming it’s not going to be made of finest cheesium.

Whilst that's a risk, any hardened tool is likely to shear off rather than bend and deform.  So if it snaps you can blame it being chinesium, but in reality an expensive one would probably have snapped too.

The helicoil will have a finished internal thread of M5x0.8 so the tap which corresponds to that size will be larger as it's cutting the thread to accept the insert.

I bought a Sealey set of taps and dies because I didn't want a cheap crappy no name box from ebay. What I ended up with was a cheap crappy box of taps with 'Sealey' written on it. Basically paid double the cost of a cheap set for the exact same cheap rubbish.

I'd go with the above advice of buying a decent holder and adding dies as and when you need them.

That linked is a thread chasing set - used for repairing bruised or where there's paint etc in the threads. It won't cut new threads.

A good brand is Dormer.

Make sure you are 'square' at all times, don't force the tap/die and certainly don't snap the tap as you can be in a whole world of pain thereafter! It's a fairly skilled task to do it well - watch plenty of YouTube videos and familiar yourself with the process.

For maximum respect from old school engineers like me - have a well thumbed Zeus guide in your tool cabinet.

Try to buy HSS, made in UK.

Dormer,

Presto

Goliath

Zeus book is a good shout. (Mine is also well thumbed).

Not heard of any of those companies before so thanks for that.

A handy thread gauge turned up with another order recently. Will print off the Zeus and keep with.

You will find one of these very useful

https://www.chronos.ltd.uk/product/combined-screw-pitch-gauge-metric-whitworth/

Will print off the Zeus and keep with.

Plastic coated versions are a few quid on eBay / Amazon / local toolmongers

As above I would just get what you need. I do a lot of tapping up to m20 and beyond. There is a marked difference in the quality of the thread you end up with v the quality of the tap/die. Brand wise dormer are ok. YG are my favourite. Spiral point if I can but if you are hand tapping spiral flute or straight flute are stronger for smaller diameters. If you are hand tapping without a centre it can be easy to break smaller diameters but probably not if you are just cleaning threads up.

If you need dies go for split dies so you can take a run up at the size and keep adjusting until you get the feel you want.