This is an M3 spiral fluted tap, these are great for tapping holes for mounting TO-220 packages for big transistors mosfets diodes or regulators etc.. and such to aluminium heatsinks (see photo for example).
Drill a pilot hole 2-2.5mm diameter, then run through the tap, I just use my drill at a slow speed, none of this hand tapping m'larky (note you must drill the appropriate pilot hole, you can't go from scratch and drill the whole hole with the tap, it don't work that way).
The spiral flutes draw out the swarf like a drill bit would instead of just chipping it out and filling the hole like a normal tap, quick and easy.
Just cheap chinese taps, HSS, no other specs, it is what it is.
Best for soft metals I think generally for spiral fluted taps, but I'm not an engineer so don't ask me about that sort of stuff, I do electric pixie wrangling, not metal mangling.
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