Bill Greenwald made this ascender long ago, and gave it to me at the 2007 NSS Convention.
The Greenwald is 73 mm. tall, 69 mm. wide, 32 mm. thick, and weighs 335 g. It consists of a U-shaped shell made from 2.8 mm steel, a cam cut from 12.5 mm. aluminum, a needle bearing for the cam, a cam pin and retaining clip, and a cam closer made out of a piece of stiff wire and a section of bicycle inner tube. The inner tube acted on a flat on the cam (below the pivot hole), acting to close the cam. The short cam face had four Z-shaped teeth.
As I recall (and I may be wrong about this), Bill used this as a foot ascender. He tied the carabiner and brake bar to his foot with webbing, and the ascender pivoted on the top of the carabiner.
I can only imagine what heavy cave mud would do to the needle bearings.
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©2008, Gary D. Storrick