Help! I need help with Helicoil
 

Heres my situation.I have a 2007Mustang GT5-speed manual witha 12mm x1.25 thread pattern on the shifter.I purchased a Hurst Classic style shift knob stupidly in a 12mm x 1.75 thinking at the time thats what the correct size was(also after contacting Hurst i found out they do not make a shift knob to fit the newer Mustangs yet). So not being the correct size i went out to Car Quest and i bought 12mm x 1.25 helicoils, i didnt opt for the kit being that it was just about $100.00 and i didnt want to spend 3 times the shift knobs cost on trying to make it fit to me thats just silly lol. So anyway to make a long story short the Helicoils that i bought do not tell me the drill size or tap size....so i was wondering if anybody knows what the correct size would be. Thanks in advance!!!