I picked up a (slightly damaged) 17.5" mirror in a sale (dirt cheap). The guy insisted it was a Coulter. How he was sure, I don't know. I didn't get a chance to ask.
It's has a f/4.5 ratio, which I measured myself.
Anyway, the side of this 17.5" mirror has a marking:
Jason Stahl #788 -5
The -5 is circled.
Does that mean anything to you?
In lumine tuo videbimus lumen.
8O Home-made 10” Dob / Home-made 4” refractor
EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm