@mR_CaESaR might be able to help I know he loves his Astro's I can;t even get to my NAC its buried at the back.
There is an illustration in the NAC manual which you can easily get online page 32/33. Looks to be M4 or M5 it isn't entirely clear but should be obvious if you have them in your hand, I guess being in the US and the fact it is metric is where the real issue lies.