You can use this thread to find the correct crystal. In your case it's a 5072. Depending on the case material, you'll want PZ5072 for a steel tension ring, or PX5072 for gold.
I also have a 166.020 that doesn't have an original crystal. Unfortunately these are selling for $150-200 on eBay, which is bonkers. The compatible ones are like $15.
I’ll let Archer or another watchmaker confirm whether this is correct but my view is generic crystals are a bad idea on the unishell DeVilles such as the 166.020 as the tension ring has a specific shape to hold the dial securely. Every time I’ve tried generic crystals they haven’t fitted well.
I confirm. The crystal ref is PX5072 with a golden ring an PZ5072 with a chromed ring.
According to the Sternkreuz catalogue, replacement must be XAC316.597 and XAG316.607
Thanks the dial appears to be held in place with a ring the damage high dome crystal on it has a chrome tension ring but the watch also a removable bezel
Looks like it’s been bodged !
ive had good experiences with the sternkreuz crystals that they specify as a replacement for the omega ones, I have used them in SMDV cases and cosmics and dynamics, sometimes when you can only get NOS omega ones, even though they are new, they are still decades old, so went brittle anyway, in that sense I prefer a new crystal even if its not an omega one when I dont have access to new omega crystals.
Thanks I’ve ordered one from cousins looking at what’s on there they have used two tension rings with the crystal being held on with the bezel
A real bodge