For those interested in convertible lenses you might search B&L Protar VII / VIIa, Zeiss Protar casket set, Taylor & Taylor Hobson Cooke XV / XVa, Gundlach Convertible, Turner Reich convertible and Wollensak series 1 / 1a.
Other companies made convertibles as well but these come to mind.
A casket set refers to a set of cells of different focal lengths that make different lenses depending on the combinations used. If you bought a set you may have 5 sets of cells and a universal barrel that in different combinations would give many different focal lengths. Clever!
I previously had a B&L Zeiss Protar in a Compound 4 shutter. I also had 3 different Turner Reich lenses in Betax shutters. The Protar and one Turner Reich were similar combinations to my Cooke, 13, 25 & 19 inches. I wish I still had the Protar.
Here are four images shot with the Protar which was most likely made in the 20’s.