Originally Posted by Big Will 85
If you're ever REALLY unsure - just go 1mm under the size of the M
That's not a particularly professional thing to do - just gets you out of a tight spot
tried this when i was trying to drill a hole for M1 x 0.25 tap, can't get the tap into the hole tho!
easy way to remember, if your tap says M12 x 1.75 for example subtract the 1.75 from the 12 to give the tap drill size, in this case it'd be 10.2mm