PZ vs PX code crystals

I find myself looking for a replacement crystal for a 568.011 c-case and some searching leads me to looking for the 5108 crystal, however I have come to find that there are both PX and PZ varieties out there, can anyone explain the difference between the 2?

Edit: I feel like quite an idiot, realised just than that its the gold and silver tension rings.

I wasnt sure if it was about the crystal height, but I must have gotten a 5107 which is why it is not fitting, the ebay listing says 5107 and 5108 in the listing

Exactly, and that's why when people ask for a crystal part number (or crown for that matter) you need to always specify the material/colour of the case.

What code is the rose gold ring by the way? - I wonder how rose gold is handled

The full set is:

PW - black ring
PX - yellow gold ring
PY - pink gold ring
PZ - steel ring