14mm should be around .5000 inches or 1/2 or 31/64 should be close..
I assume you are tapping.. what size thread 1.25 or 1.5 as they call out different size drill bits..
Plenty of tables on the web, as FYI, but it comes down to whether its 14mm* 1.25 or 14mm * 1.5..
Not an answer but should get you closer..
http://www.korit.com/tapndrill.htm
VR
Alex