I have an FP15 system, the FP1 transmitter and the FP5 receiver. Includes was a rubber strap. What is the intended use?
Similar to the Velcro strap included with some Shure wired microphones, the FP rubber strap has multiple uses. The rubber strap could be a cable wrap. It can be used to attached a transmitter or a receiver to a the round leg of a camera stand or loudspeaker stand; the rubber strap creates the friction needed to prevent the pack from sliding down the pole. In essence, the rubber strap is an accessory that has no specific use, but multiple general uses.