Aluminum heads and spark plugs

Exposed threads will carbon up. Carbon is HARD & the SOFT alum will not be amused when somebody tries to remove the plugs. I had this problem of exposed threads with another brand of engine & even with the recommended 3/4" reach plugs, several threads were exposed. Very bad design.
I machined about 3/16" off the end of the plugs so that there was no thread for carbon to clog up....