- 3-A Sanitary Standards for Sanitary Fittings, Number 63-03 (Authorization number 621).
- 3A sanitary finish ID and OD
- Please note in sizes 1/2" through 12" pipe is known by its nominal inside diameter, which differs from its actual inside diameter. To distinguish pipe sizes from actual measured diameters as used for tube, the terms iron pipe size (IPS) or nominal pipe size (NPS) are usually used. For all pipe sizes, the outside diameter (OD) remains constant; the variations in wall thickness affect the inside diameter (ID).