I don't know how much compression difference .004 would make. I would lean towards .021. Maybe some one with more knowledge than me will chime in.That's weird. My Stihl kit 1122-007-1053 has both that are .5mm . Now after looking at it closer this must me a gasket to fit 2 different saws and I also noticed there is 3 crank seals and the bolt pattern of the base gaskets are different so I answered my own question. So after seeing that there really is only the squish option for .021 kit gasket or .017 Stihl. What would you pick? .017 a little to close for comfort on a plain jane build?
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