It looks home-made to me, too. More than 30 years ago, in UK, I put a central heating system into my house. IIRC, it used radiator valves whose spindles had a flat end, like a thick screwdriver blade. The plastic knob pushed onto the flat. Sometimes, with a too-stiff spindle, the knob fell to bits. IIRC again, the balancing valves were the same, but had a cap, rather than a knob. When balancing the system, I used either a spare knob or a small adjustable wrench (with trepidation) to turn the spindles. This gizmo would be a better way, if there were enough room to swing the T-handle. I suggest it’s for a similar type of application.