M8 thread with a 1.5mm pitch?

I've been tapping a whole heap of holes for my recent CNC build. For an M8 thread with the more common 1.25mm pitch, a 6.8mm hole is the norm (you sure it's a 1.5mm pitch? as this might account for why your tap is getting stuck!)

http://www.efunda.com/designstandard...ewm_coarse.cfm