This aircraft safety personnel restraint is a high-quality product manufactured by Aerial Mach & Tool in 1971. It is designed to ensure the safety of personnel on board during flights. The product is made with excellent craftsmanship and attention to detail to meet the highest standards of safety in the aviation industry. With its durable and reliable materials and construction, this restraint is a must-have for any aircraft. Whether you are a professional pilot or an aviation enthusiast, this product is the perfect addition to your collection of aviation parts and accessories.

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Not sure what type of aircraft this may have been for, but I think it was possible for a Door Gunner in large aircraft maybe C-130 or C-5's maybe this was used to strap in the cargo load master while deploying/releasing stuff out the back end of the aircraft not so sure however look it over and YOU decide for yourself what this Harness Personnel Restraint  P/N 3590018-105 might of been used for.

(MILB-1)