Arca Swiss exact sizes

Now here's an interesting one. I'm in the process of making a leather bellows for an old arca swiss f-line 5x7. Obviously, sizes of he bellows frames are quite critical. Initially, I had envisioned hacking an existing frame for the front and a new one for the rear from aluminium sheet. However, I figured that once I would be cutting sheet anyway, I may as well also cut a front frame. In comes the surprise. Running a quick measure with my rusty callipers, the following come up.

Rear 5x7 bellows frame:
thickess 2.5mm
outer 215mm
inner 187mm
(frame 14mm wide)
corners rounded at 90 degrees 8mm


Lens plate measured for front frame:
thickness 1mm
outer 110mm
corners rounded at 90 degrees 5mm

Well, so far so good, no surprise here... Then I traced these dimensions on paper so I could trace them onto the respective aluminium sheets. Of course I do the outside cuts on my rotatrim. But then...

The carefully traced paper dummy of the 110mm lens board is up first. I cut it, all good. However, on the rotatrim scale that is meant to be accurate...

110mm lensboard outer 110mm (?!). I of course put a real board on it and sure enough, I'm 2mm short of 110mm on that too. I find this rather hard to believe as everything arca always seems so meticulously and flawlessly executed. To solve this conundrum, I would be much obliged if someone more knowledgable than myself could give me te exact measures of:

The 110mm lens board (which I will assume is 110mm except my rotatrim thinks otherwise)
The exact dimensions of a 5x7 bellows frame (f-line)

Thanks a million for this and have a great day!

check your rotatrim scale. Mine is NOT accurate.
Arca ain't perfect, but they're pretty darn close :)

Yes, so it seems, the 110 in the post was of course 108mm?!. I am a little puzzled now. I'm sure arca, like anyone else works with an acceptable error margin. However, I doubt all boards are 2mm off their specification. If only I had kept the ruler that I used in high school decades ago... Now there's no testing. I'll just go with the calliper measurement, disappointed in the rotatrim though. It's a pro model and not cheap (particularly in Europe). It cuts film well though.

About a decade ago, I made a half-way thing....combining an old 215mm 5x7 rear standard-frame with an F-line 171mm front standard. So, if bellows sourcing is your issue, you can modify an old-type bellows quite easily to fit the newer frames.

An aside: If you have any info on getting good bellows: My leather w/a bellows are getting a little bit old now and I am interested in finding a new alternative for either camera series. Thanks.