This lightweight aluminum device consists of three bollards and a cross piece riveted to a subtriangular piece of sheet metal. The lower bollard is 38 mm. in inner diameter, while the upper two 11 mm. The lower bollard is cut away on the upper side, although it isn't clear to me that this is necessary or desirable (except to save weight), since it leaves some sharp edges that can damage the rope. These can be removed with a file.
The device is rigged by inserting a bight between the upper bollards and looping it over the lower bollard, then clipping the seat maillon through the lower hole. I find that the back of the device bends noticeably in use, but not enough to damage the device. The resulting friction is less than I would prefer.
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©2007, Gary D. Storrick