so i was talking to my girlfriends dad tonight and he used to be into planes back in the day, and i was talking about my OS TR .12 and he said whats a .049 compare to that and i said well i belive the .049 is huge. he said how big is the piston, and ive never seen the inside of my TR so i said well the piston on my .15 is about 1/2 or alittle smaller, and he said is .049, meaning .490 thousandths which is almost 1/2 inch. So what exactly does the .12 or the .15 stand for?

Actually an 0.049 is tiny it is a direct comparison to 0.12 (cubic inches)

.049 is what they use in cox planes. there real small.

yea i had a cox helicopter that used no radio and you just let it go, well it went.... never found it though my friend found the dinky engine in the lake bank like a mile away... should of used some string lol :p

thanks guys! :)