I have a RCGF 40cc twin.

What is the recommending gap settings for the NGK CM-6?

I didn't look it up, but memory is saying .025? You could do some digging around on the NGK site to be sure, but that's a pretty safe bet.

It's around .7mm

The width of an Xacto blade works well (.022).

It depends on the ignition the plug is hooked up to. 0.4 to 0.6mm. Standard, the plug is gapped to 0.5mm

X-acto blade works pretty darn well

Gap each plug for a twin so gap is exactly the same. .025 with-in .0000000000000001

0.5mm=.01969.

#11 X-acto Blade and you will never go wrong.