This pair of heel restraints was used in the Apollo 14 command module during liftoff.
They were used to secure the astronaut’s feet in place during the violent early stages of the Saturn V launch to prevent injury.
The restraints are made of a very lightweight metal and heavy duty stirrup straps with Velcro closures.
The items were manufactured by B. Welson Co.
I was able to acquire these heel restraints directly from Apollo 14 Lunar Module Pilot Edgar Mitchell.