RAM® Pin-Lock™ 4針安全旋鈕（適用於C尺寸及擺動臂）

Installed this on my C size RAM mount to replace the old plastic knob, and the metal construction feels much more secure. The keyed lock is a nice touch for preventing theft in a truck cab.

Wish I'd bought this sooner—the keyed removal means my gear stays put when parked at job sites, and swapping it onto my 1.5" C arm took about two minutes. The threads engage smoothly too, so no wrestling with a stripped knob.

The security knob feels solid and the key mechanism locks in with a satisfying click. It swapped straight onto my 1.5" C size arm without any fiddling, and the 5/16"-18 threads are clean and tight. Exactly what I needed to keep the swing arm from wandering.