RE: confusing imperial system
Yeah, they don't make a 6.2mm... just a 1/4" and a 6mm... take a look at these two Dubro spinner nuts, Tower lists the compatible engines on each of these pages... these Dubros are one of the best spinner nuts IMO...
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXE158&P=7]Dubro 1/4-28 Spinner Nut[/link]
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXE160&P=7]Dubro 6mm Spinner Nut[/link]