Filters for Petri f1.9?

[groupw]

Hi there, I am new to this forum. I tried a search and could not come up with what I was looking for. I have a Petri f1.9 Color Corrected Super. The fixed lens does not say what thread size it uses for filters. I'm guessing it is in the low 40's mm, but am not positive. I do not have a good camera store around here to take it in and test-fit. Anyone know what size filter rings?

 

[groupw]

Thanks for the help!