This is the Bausch & Lomb Baltar 75mm f2.3 lens as I got it. There is a thread mount, which I understand is a Bausch & Lomb specific size. There is no focus ring, and a very firm aperture ring. The front of the lens has a yellow and pink dot on the front.
I mounted the lens with Apoxie resin (coating the threads with machine oil to make sure it can be removed), into a M52-M42 17-30mm Helicoid Macro unit. This allows me to achieve infinity focus (plus a little extra past infinity), and up to about 12 inches MFD (minimum focus distance).
Here is the lens connected to a Fujifilm X-E1 with a Fotodiox M42-Fujifilm X adapter
Tiger Swallowtail – Sigma SD9 + Baltar 75mm 2.3