I have two shutters, with the same lens mount. The two cameras i got came from the same person and he appears to have shared one lens between them.

One shutter has two brass "L" hooks that twist and release the front to expose the inner works. The other, marked as a "Sanderson shutter" has a front that is somehow fixed and not easily removable. There is a screw on the side that has no apparent purpose... perhaps that holds the front on, I don't yet know.

Out of curiousity, I searched the European patent office for Thornton-Pickard shutter patents. I found several describing "improvements" to the roller-blind shutter, but I couldn't find the original 1898 (I think) patent.