those plastic things work well and is a good quick reference, if you don't have the tools. I have one hanging on the wall and use it more than my pitch tools, etc. Just wish it were metal or a better composite/plastic, etc. But it was free so...
EDIT - I see that one doesn't have pitch gauge on it, although maybe it's on the back side on yours? (mine's on the front side)
If it's 10 mm dia then chances are it's 1.25 pitch, since mitsu uses that oddball size all over the place. I say oddball, cause the most common 10 mm is 1.50 pitch and it's much harder to source 10-1.25! 8-1.25 is pretty common and used in many places, also.