I acquired my Rose Mfg. Safe-Hi from Theresa Williams and Maury Benamy in 1995.
My Rose Mfg. Safe-Hi is 150 mm. long, 300 mm. wide, 58 mm. high, and weighs 963 g.
The Safe-Hi consists of two stamped steel plates with a third plate welded to one of the others. The two main plates have a U-shaped notch in one end and two "curls" at the side of the notch. The curls on the two plates nest. The plate with the inner curl has a bend so that it sits about 20° away from the straight plate. The straight plate has a dimple near the notch. The other ends of the plates have punched holes that admit a 1/3" (12.7 mm.) braided rope. The third plate is welded to the straight plate so that its hole is offset enough to keep the rope from freely sliding under light load.
The straight plate is stamped as follows:
USE ON ¾IN
DENVER, COLO .
The Rose Manufacturing Safe-Hi is an old design that is so different from anything else in my collection that it took me a long time to figure out how it was rigged. The device can be opened by releasing the rope catch (blue arrow) and pulling a lot of slack into it. The two main pieces can then be separated, using the two "curls" (green arrow) as a hinge, and then sliding the two pieces sideways to separate them completely. The main line is placed in the notch, and the two main pieces are reassembled. The rope is now running along the path indicated by the red arrow. The lanyard is pulled tight and held their by the rope catch.
When the worker takes the attempted suicide plunge, the lanyard tightens and pulls the two main pieces together. This squeezes the main line, bringing the worker to a stop and averting the big splat. The instructions on the device indicate that 15 feet (5 meters) of clear space are needed for this to happen.
I don't see how this principle could be used in a working ascender, but perhaps a rappel safety could utilize the idea.
The Rose Manufacturing Safe-Hi is protected by U.S. Patent 2,914,139.