I don't buy complete tap/die sets, just get set of 3 the size you need (taper/second/plug)
Probably be 10x1.25.
Get HSS they last much longer than Carbon steel
You may be able to remove Helicoils and screw studs straight in, 8x1.25mm Helicoil probably uses 10 x1.25 'hole' (may be 9.8mm, I forget)