NASA photo below shows astronaut Fred Leslie using this type of holster to secure his Remote Communications Unit to his left leg during the STS-73 mission.
Photos below show the front and back of the 5 available holsters.
#5: Used in training (with significant wear on straps).
Red lines through label indicate it is not to be used for flight. Sometimes items used in training were previously flown, but there is no record of flight status for this holster.