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heightec D31 Prism

Front Rear
Front Rear
Side Open for Rigging
Side Open for Rigging

Technical Details

I acquired my heightec D31 Prism on eBay from the American Alpine Club Store in 2017.

The heightec D31 Prism is 239 mm. tall, 78 mm. wide, and 31 mm. thick, and weighs 510 g.

The two side plates are made of 2.9 mm. aluminum. One side plate pivots to allow threading the rope. The lower ends of the side plates are bent to converge at the attachment point, which consists of a 16.1 mm. wide, 25.7 mm. high hole on the fixed plate and a slot on the other. Neither of the attachment points are beveled. The upper portion of the slot is covered by a plastic gate. The gate pivots on a steel rivet, and a spring set in a deep slot closes the gate. With the gate closed, the opening is only 19.6 mm high.

The lower bollard is part of an autostop assembly. It is a stainless steel casting fastened to a handle made from 2.9 mm. aluminum. The lower surface of this bollard has an 11.3 mm. wide, 3.1 mm. deep U-shaped rope groove. The right surface is flat. A 24.8 mm. tall steel anvil is riveted to the rear plate opposite this flat surface. The handle and front plate pivot on a rivet attached to the fixed side plate side. The handle has a "rubbery" plastic cover for comfort. Friction from the main rope's passage tends to turn the lower bollard and force the flat face towards the anvil, thus locking the rope and ideally arresting the descent. The rappeller uses the handle to keep the autostop feature disengaged. An extension to the handle has a friction block riveted to it. When the handle is squeezed too far, this block forces the rope against the upper bollard.

The upper bollard is turned aluminum. It is 36.3 mm. in diameter with a slight15.4 mm. wide U-groove that reduces the internal diameter to 35.3 mm. The bollard is eccentrically mounted on a rivet through the side plate, and spring-loaded to rotate counter-clockwise toward an 11.7 mm. pin riveted to the lower left of the bollard.

The pivoting side plate is printed with "D31," "Prism Descender," "080611," "019," "," "CE0120," a book-with-an-"i" icon, EN341:1993 (B)," "EN12841:2006 (C)," "¤", "Ø 10.5-11.5," "EN1891 (A)," a human icon, the outline of an up-pointing arrow, "Max 200kg," "Max height 100m," and a rigging illustration. The inside of the rear late is printed with an anchor icon, and arrows and rope illustrations showing the rope path for rigging.


The Prism is well-made, but too heavy for my taste. As much as I dislike auto-stop descenders (for a variety of reasons), I dislike double-stop descenders even more. It is very difficult to design a simple double-stop descender that is not strongly affected by rope diameter. I tried the Prism on 11 mm. PMI Pit rope, a very "standard" American Caving rope, and found that it not only had too much friction for my taste (I "weigh" over 90 kg.), but I also had difficulty finding a balance between descending and avoiding actuating the double stop feature. This is not going to be one of my normal caving descenders.