compression tester for 115 4 stroke

[hwoodyone]

I need to check my compression on my 2001 115 4 strokes. I want to get a compression tester but need to know the right thread size.
Can someone advise me as to the correct item needed? Oh! I am about 400 miles away from my boat so I can't pull plug to check.

[hwoodyone]

Thanks very much!