Plumber's Thingummy Jigs

Casting about to try and find something for the "never seen that before" challenge I went into the boiler house where we store light bulbs, Jack's tool box and a miscellany of many items we never use, and I spotted these brass fittings which must have been left by the plumber.  I'm guessing they might be used on radiators but anyway, I can honestly say I've never seen them before.

Thank you intothehills for coming up with an unusual challenge and thank you for the response to my MM blip yesterday, it's very much appreciated.