do gasket mm sizes matter? like for cylinder to case gasket, does the mm
size matter?

The gasket size determines your x demension. There should be 4-5 different gasket thicknesses for most KTM's. You have to measure with a set of calipers. Yes, it does matter.
Little Jeff

lol well thats not good, im not much of a mechanic, but i flooded my engine with muddy water when i fell over in a huge puddle, i took apart the carb, top end, reeds, and flushed the crank with gas/oil, cleaned the exhaust, pretty much did everything, but obviously i had to take off the cylinder do i had to replace the gasket, i didnt know there were different sizes before i went to the shop, i didnt know what to get so i just got a 75mm gasket (the thickest one). i put everything back together and now it wont start, i used starting fluid, checked the plug, and gas, and everything seems to be fine, but it wont even kick over, any idea what could be wrong?

If everything else on the bike is fine, then your compression is to low becasue of the thick gasket you used. You may need to order a thinner gasket.

damn lol well hopefully thats not the problem, but thank you for your input, once i get a new spark plug and really go over everything ill definitely consider replacing the gasket