I acquired this descender from PetrenkoWorld in 2007.
The Half Crab back plate is a piece of 5 mm. steel cut to shape and having the right side bent backward about 45°. The left side has a 14.2 mm. attachment holes at the bottom and an auxiliary 14.2 mm. hole at the top. There are three steel bollards riveted to the left side of the back plate at 40 mm intervals. Each bollard has a 15 mm long rope section and a clearance notch (formed in conjunction with a flat washer) for a swinging cover plate. The rope sections are 18.8 mm. in diameter at the plates, and narrow to 17 mm mid-channel. The cover plate is a piece of 4 mm thick, 27 mm wide strip steel. It pivots at the top bollard and has notches to engage the clearance notches on the two lower bollards. The bottom of the cover strip has a 13.9 mm hole that aligns with the lower hole in the back plate.
The right side of the back plate has a 12.2 mm. long, 20 mm. diameter bollard and a 87 mm long, 24.5 mm. wide, 4 mm. thick rope retaining plate attached (presumably riveted). The top and bottom of the retaining plate are bent outward about 25°.
The Half Crab weighs 662 g.
The entire device is painted with with something that gives a mottled gray-and-black surface. There are no markings on the device.
The rappeller rigs the Half Crab by opening the swinging cover plate, slipping a bight over the middle bollard, closing the cover, and securing it by clipping through the basal holes. The user can get extra friction by looping the rope over the right-hand bollard.
I do not like the painted finish, since it will wear off and leave a mess on the rope. The Half Crab is also too heavy for my taste.
I do not know whether there is a full crab.
FixedMulti1095.html/070520
©2007, Gary D. Storrick