Reducing the size of the head tube is known as one of the chemical fittings for connection of two different diameters. Head size is divided into concentric and eccentric head. Diameter pipe diameter pipe materials including stainless steel, alloy steel, carbon steel size head diameter pipe, steel q234q345 diameter pipe on the 20th and so on. Product Standard GB American Standard British standard and non-standard high-pressure stamped "made of steel pipe fittings" quality requirements GB / T13401-2005 the standard diameter pipe diameter pipe should be consistent with current national standard "welded steel seamless pipe fittings "GB / T 12459-2005 standard GD0506 ~ 0507 Ministry of National Standard (GB / T9112-2000) machinery of the standard (JB81-59, JB / T74-94) Petrochemical Department of Standards (SH3406-96) Ministry of Chemical Industry Standard (HG5010- 58, HG20592-97)