We've had some discussion before about the type of face used on UG moonface moonphase discs. You mostly see one type, but there's some variation. This is the most common type (connected eyebrow and nose): But there's another variation you see sometimes (disconnected eyebrow and nose) which looks like this: That second one belongs to @rolokr Anyhow I recently found a similar example in a box of UG parts. Aside from the different face, it's also thinner, and I think a touch larger (need to check with calipers). These pics show the thin one next to two "standard" examples from a cal 287. So two questions..... 1) is this just an acceptable variation on UG moonface (I lean towards yes) 2) what does the thinner version belong to, is that for a triple date moonphase instead of a chrono? I've never compared the discs side by side before, but I have been told by my watchmaker they are not interchangeable.
For our records the thicker moonphase disc above (cal 287) is 7.5mm diameter and 1.15mm thick the thinner moonphase disc is 7.9mm diameter and 0.6mm thick. my watchmaker said he could not be 100% sure without having the disc in hand but felt relatively sure the slightly larger and thinner disc is a UG disc and that it belongs to a cal 291 (triple date moonphase) as suspected. Interesting that the two examples above are Tri Compax, and not triple date moonphase. If this theory is correct then it means this alternate face style is used in multiple calibers.
I think the variation goes along with what we (think we) already know about UG visually: Differences in dials are not necessarily alarming, so inconsistency among moon faces wouldn't be cause for alarm either. I think it's also generally accepted that the service discs were without face, but the size and thickness should be the same for the same calibres.