FWIW that adapter is a POS from a signal loss perspective. The only reason they appear to work is because even with a 10db loss in the adapter going from a ducky on the handheld to an external antenna still works better. Inside the metal case is nothing but a $.025 1/8" audio headphone jack.
For a more effective and far less expensive approach mount a bulkhead BNC barrel connector somewhere low on your panel, connect the external antenna to the backside (behind the panel) and run a short coax from the front (pilot) side to the radio that normally connects to the external antenna. When you want to use the external antenna with the handheld, disconnect the front coax and connect a 5-6 ft coax (BNCs on both ends) between the bulkhead BNC and the radio. The signal loss with that arrangement is a a fraction of one db.