19mm or 3/4-inch automotive coolant reservoir cap

This is a simple coolant cap for ¾ " or 19mm quick connect coolant ports on automobiles.  I made this to stop drips while working on cars, it may still seep due to the pores but that doesn't bother me.  This is not for permanent use there is nothing to retain it on the vehicle, this is just for use while working on the vehicle.  It will not work on barbed fittings, only smooth shank fittings.  It uses a R-13 o-ring, my box of o-rings says that is ¾" id, 15/16" od, 3/32" cs.  Looking online this may actually be a metric o-ring that is labeled SAE as a R-13 o-ring comes up with very similar metric dimensions.  I added a picture of a sample fit up for it.

I printed the cap with the closed end down it leads to some stringing when it does the o-ring recess area.  It could be played with to orientate it or support it to stop the stringing but I found it works fine as it is after you trim the strings.