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IMO Extension Arm
(#625, 1896)

Extension Arm Mounted on Gibbs Ascender
Extension Arm Mounted on Gibbs Ascender

Technical Details

I acquired my IMO extension arm from Inner Mountain Outfittersat the 1987 NSS Convention. I acquired another in 2017 as part of Bob Thrun's collection.

My IMO extension arm is 25 mm. long, 178 mm. wide, 10 mm. high, and weighs 97 g.

There are no markings on the extension arm.


In the late 1970s and early 1980s, a number of people were looking at the Gibbs ascender as the basis for a rappel safety. I dislike the idea of using a Gibbs as a rappel safety for a variety of reasons, but others thought the idea had merit. The spelean shunt was one popular idea, but some people considered it too hard to release. Some of these ideas used special cams with levers on them (for example, the Charlton Lever Cam). Alex Sproul of Inner Mountain Outfitters developed this attachment that easily fits on a quick-release pin Gibbs ascender. It allows one to release the cam under load by pulling on the lever, or by attaching a carabiner and sling to the lever and standing in the sling.