We had originally thought that these were collar studs but are delighted to have received the following information from a retired nurse.
"I just thought I would mention they are not actually collar studs but are cuff studs. A lot of the Long sleeve nurses uniforms would have detachable cuffs which were frequently removed and often changed and attached via a pair of studs; the unusual mechanism you mentioned would be for quick changes of them using only one hand."
I did my nurse training in 1970s and well remember these items on some of the more mature seniors nurses uniforms who refused to move forward with more modern uniforms."
Box of 4 individual studs, so two pairs
Made in England. These are original vintage items.