IKEA GRILLTIDER cap with 6mm o-ring seal

I redesigned Dierre16's (IKEA GRILLTIDER cap by Dierre16 - Thingiverse) IKEA Grilltider cap to fit a 6mm inner diameter o-ring as a seal. 

the o-ring is an approx. 1.4mm diameter rubber, making the outer diameter just shy of 9mm.
i used a toothpick to get the o-ring in there, which was a bit fiddly but now it sits snug and won't come off.

prints flat as provided, i made it 0.2mm but try another, it doesn't cost much time or filament!
i used normal supports on buildplate in order to avoid cave in in the cap. i generally use a 0.25mm z-distance from the support to the model and was able to easily grab onto it using my flushcutters which removed it easily!