Parveen Industries Pvt. Ltd. Offers Silver Subs Black Nut Hammer Unions. The Silver Subs Black Nut Hammer Unions falls in the category of Treating Irons, Unions, Swivels and Circulating Heads. Parveen Industries Pvt. Ltd. Is an ISO 9001: 2000 certified company. The Silver Subs Black Nut Hammer Unions have wide range of applications, including steam service and line connections. These unions are provided with a bronze seat in the female for the effective sealing and prevention of rust formation. They are suitable for 6000 PSI CWP.