Dixon 12" National Pipe Tapered (NPT) Carbon Steel Flange.
ASA Forged Flanges have raised shoulder with no raised face.
National Pipe Tapered is common in plumbing and some industrial uses. Sometimes referred to as “pipe thread” because PVC pipe and schedule 40 pipe are typically threaded in NPT.
ANSI was originally formed in 1918, when five engineering societies and three government agencies founded the American Engineering Standards Committee (AESC). In 1928, the AESC became the American Standards Association (ASA). In 1966, the ASA was reorganized and became the United States of America Standards Institute (USASI). The present name was adopted in 1969.