This double socket arm is the middle piece of a ball and socket mount. A ball goes in each end, one on the chair side and one on the device, and a single knob locks both joints at once so you can set a speech device, a switch or a small holder exactly where the client can reach it.
Loosening the knob lets the arm move freely for repositioning, then one turn locks the position again. That is quick enough for a carer to move a device out of the way for a transfer and put it back without calling a technician.
It is machined from marine grade aluminium in black and sized for light devices, which covers most communication and switch mounting an occupational therapist sets up on a chair.
