hi what size compression test fitting do i use for a honda civic 1996?

14mm 16mm or 18mm?

 

oh c'mon. no one knows? i've heard that you should use the 14mm size fitting. I know for a fact the spark plugs need a 16mm socket to get out. just seems odd you'd use a 14mm fitting when testing compression

 

Use whatever size that fits into your spark plug hole, it hand tight and size is not based by your spark plug bolt size. Maybe I'm not clear of your intension.

 

The spark plug holes have standard 14 mm threads, same as almost every other car. The fitting that came with the gauge should work with no adapter.

The hex drive on the plugs is 5/8 inch, which is almost exactly 16 mm but it is actually made to inch size. That has no relation to the size of the threads of course.