Metal.: Copper Alloys Couplers are counter bored to completely enclose threads & protect from damage and corrosion. Size mmProd. CodeProd. CodeProd. Code BrassAl. BronzeGunmetal 14 HEC 14 HEC 15 HEC 15G 16 or 5/8" HEC 16 HEC 17 HEC 17G 19 or 3/4" HEC 19 HEC 20 HEC 20G