GrandeGixxer,
To use the Helicoil inserts you bought, you will need the special tap for them.
McMaster Part #91709A355
Screw Thread Insert Tap M3-.5 Internal Thread, Plug Style
$ 16.22 Each
The procedure is to drill out the existing 3mm holes (McMaster's site calls for a 3.2mm bit).
Then you use the special tap above, insert the helicoil with some red loctite and your back in business.
You might want to enquire with McMaster's as these things usually come in a kit that contains a few inserts, the special tap and a tool for inserting the . . . errr . . . inserts. The same tool is also used for breaking off the tang. I'm not sure how you might get a fiddly 3mm helicoil in without this tool.
It looks like the cheapest kit is:
McMaster Part # 91732A942
18-8 SS Standard Helical Insert 10 PC Repair Kit, M3 Thrd, 4.5mm L, .5mm Pitch
$ 50.06 per Kit
. . OOOuuch.
