A pair of plastic maternity clasps, used to make drop down cups. The size indicates the strap width which should be used.

two sets in pack, to make ONE bra.
The first number is the width of the strap that attaches directly to the bra, the second is the width of the Original bra strap. Measure the width of your bra strap and choose a fitting with the second number close to this width. I.e - USE THIS FITTING WITH A 16-23mm BRA STRAP WIDTH

picture shows what you will receive when you purchase 1. One clip is shown closed the other is shown open (you get all 4 pieces - which is suitable to make/convert one bra to a nursing bra)