14k Yellow Gold Swivel Trigger Clasp. (jump rings sold separately, item 152882362479 is a perfect fit)
Or you can use 5mm+ split rings

These may be stamped 585 or 14k

 7mm x 12mm (1/4"x1/2")   Ring ID 1.7mm  
width includes Trigger
5.25mm width w/o trigger

Weight: 0.48 DWT (0.75 grams)