Brass. Pink version is zoisite . Mastic version is dalmatian jasper . Black version is agate . Size XS=T0= 51.5mm circumference= 16.4mm diameter . Size S=T1= 53mm circumference= 16.88mm diameter . Size M=T2= 55mm circumference= 17.52mm diameter . Size L=T3= 57mm circumference= 18.15mm diameter