I have an Arca-Swiss Bellows 8x10 frame set with 8x10 back and fresnel glass. I understand that there are two front frame sizes for this particular item, 141mm x 141mm and 171mm x 171mm and was wondering where the measurement is taken? The square opening of the front frame, according to my digital caliper, comes in at just over 142mm. The outside dimension of the entire front frame comes in at 171mm. So do I have the 141mm x 141mm version or the 171mm x 171mm?
Here is a pic of what I have. Any light you can shed on this and which measurement I go with is appreciated.