Clive. I find it best to buy good brand names. For hand tapping nearly anything will work but as they say "you pays your money and takes your choice." In short , the better quality always works for me.

regards

As your M12 is quite a hefty size you might like to consider a set of 3 serial taps, where they actually vary in size from no 1 thru no 3. Like these **LINK** These make it much easier to tap the larger threads. Plenty of cutting lubricant makes a big difference too.

A normal set of three taps only vary in the length of the taper on the taps

+ 1 for Andrews comment . The other thing with spiral taps is you can use the drill press or mill to get them started squarely , just mount the tap in the drill chuck and run the machine up to speed ( i use something around 200 rpm ) then swich off the power as you feed down on the quill . The inertia inside the machine is usually good for a turn or two and you simply undo the drill chuck and remove your part with the tap still in the hole ready for hand tapping .

If i have a few to tap on the same surface i wind the tap out while it is still in the chuck and move to the next hole , once they're all done i move the part to the bench and hand tap , the tap is guided by the first few threads done under power .

The downside is they are usually more expensive but when you weigh it up with the fact you only need one tap per size and not two or thee the cost is negated .

I don't rhink i even have a starter tap in my collection as i use intermediate to start off with when using straight flute taps and a bottoming tap if required .

I use spiral taps from 3mm up and they make tapping a pleasure ! You can also use a battery drill with them and a tapping guide to set you off straight although you need to take care as it is easy to get off kilter and snap the tap .

Possibly surprisingly but the 'economy' Metric HSS sets are usually serial type.

Look for one ring on the shank of the first tap, two on the second and none on the finishing tap.

Neil