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I acquired this rack from Inner Mountain Outfitters at the 2016 NSS Convention.
My CMC 3D rack is 171 mm. tall, 106 mm. wide, 32 mm. thick, and weighs 483 g. The frame is made from 9.5 mm. stainless steel bent into a U, with an internal width of 29 mm. There are 3 brake bars.
The top bar is a dual hyperbar secured to the frame with two 4.75 mm roll pins placed in hoes drilled in the end of the bar. This bar is 15.2 mm. wide and 20.3 mm. high inside the frame. The ears on each side curve upward for 29.8 mm.
The middle bar is a 57.9 mm. long, 31.7 mm. diameter, 3.5 mm. wall thickness tube with an internal locking mechanism. The bar slides and pivots on the frame, and notches on one end of the bar keep the bar from opening while in use. A spring-loaded red button on one end of the bar unlocks a mechanism that allows a spring-loaded black piece inside the bar to slide, thereby letting the middle bar slide on the frame, disengaging the end notches and allowing the bar to open.
The lower bar is an inverted copy of the top bar, but instead of being pinned in place, the frame holes pass completely through the bar, allowing the bar to slide on the frame.
The top bar is printed with the CMC Rescue® logo and "3D." The lower bar is printed with "MEETS NFPA 1983 (2012 ED)," "Ø 9.5-13mm MBS 13.5 kN “T”," "Ø 13mm Only MBS 22 kN “G”," "Lot# 16110-24," a book-with-an-"i" icon, the UL Classified logo, and "5F04."
Although thee 3D resembles the Conterra Scarab that I classified as a Miscellaneous Descender, the construction is that of a three-bar U-frame rack.
The workmanship on the 3D is excellent. The locking mechanism is not clearly visible and I cannot see exactly how it operates without destroying the descender, but it seemed to work well, at least on clean rope. I have not tested it in heavy mud. Naturally, my tests are not exhaustive; in fact, the day I wrote this, CMC (to their credit) issued a recall notice of all 3D descenders in Lot Numbers 16001 – 16203 because of "an unexpected release of the 3D descender's locking center bar that happened during a recent training exercise." Their "required action" is to remove any affected 3D products from service, and return it to them for a no-cost full replacement. What is wrong with a simple brake bar made from a bar or tube, drilled and slotted like normal? Complicating the mechanism so that the bar can open in ieither direction does not seem to be a good idea. The advantages seem miniscule and the risk unnecessary.
When rappelling, the 3D does not give enough friction when used as a straight brake bar (neither CMC nor I recommend doing that), but the horns allow looping the rope under a lower horn and then over the top to get enough friction. If you need more friction, you can then cross the rope to the other side and loop it under the lower horn and then back around to the other top horn (Note that these are NOT the same as the recommended method for the Conterra Scarab). The horns also make it easy to lock off.Personally, I don't think three bars on a U-frame rack are enough, even with dual hyperbars. I would like to have some more redundancy and some more friction.