Neck dimensions of flush neck flanges, socket weld flanges and threaded flanges The neck dimensions of flush neck flanges, socket weld flanges and threaded flanges of the same specification are exactly the same. The neck of a flat welding flange with neck is different from that of a butt welding flange. The neck is straight cylindrical, not a tapered neck, but a slope of no more than 7° is allowed to facilitate processing; the height of the neck is slightly shorter, and the diameter of the neck is slightly larger than that of the tapered neck to improve rigidity. The neck diameter and neck height of the inch pipe series flange with PN≤4.0MPa are consistent with ISO. In the part of PN4.0MPa and DM300~600, refer to the principle of PN2.5MPa and the neck size of the butt welding flange with neck of PN4.0MPa. The neck size of the socket welding flange of PN6.3~10.0MPa is consistent with the size of the HGJ flange. The metric pipe series is the same as the inch pipe when DN≤350, and the neck diameter is adjusted according to the difference of the outer diameter of the steel pipe for the rest. The socket depth of the socket welding flange is uniformly valued according to the socket welding flange of ANSI B16.5. The diameter of the socket hole is equal to the inner diameter of the flange with the necked flat welding flange, and the inner diameter of the socket welding flange is equal to the inner diameter of the flange with the necked butt welding flange.