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John Middendorf

Climber, Designer, Inventor of A5 and D4 climbing tools.

John Middendorf 

@bigwalls
Climber, Designer, Inventor of A5 and D4 climbing tools.

Mechanical Advantage: Tools for the Wild Vertical

By John Middendorf
The history of engineered tools for climbing and alpinism. (Looking for D4 portaledges? See bigwalls.net)

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