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Yes you drill first then tap then put in the insert. A Letter Q Drill is 8.5 MM if that helps

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I will make a note of that size. Q = 8.5 MM

what are the other 3? H,X,G ? -the chart shows them but I never know what they are and asking for them is a blank.

I keep this chart hanging in my shop. I can get the heli coil kits but rarly find the sales person knows what size bit or where to look.

I will looking for the 6.7 MM drill bit today for a 1/4-28 fine thred repair on the pinion yoke.