SECONDS: only due to the edges are not entirely smooth to touch.

45mm brooch back, with a simple hook-in clasp.  Three holes in the back bar so the glue or solder can run through. 

These brooch backs have a narrow back; use in lighter applications. 

Great unit to glue your ideas on to. It can be used for a lapel Brooch, hat Brooch, a badge Brooch, a school Brooch, a club Brooch, etc.
Glue interesting things onto it, like fabric, feathers, lace and beads. 

Use epoxy glue for max strength, rough up the surface a little first with fine sand paper.