Reading the print line on pipe

Entry in Sizes, codes and marks · Updated October 29, 2026 · Written by the Know Your Pipes editors from the sources listed under References

Pipe markings are the printed or stamped text a manufacturer runs along a length of pipe or tubing to record its material, size, governing standards, pressure rating, certification marks and production code.^[1] Reading them is usually the quickest way to tell what a pipe is and what it was made for.

1 What a print line contains

The content is set by each product standard. For PEX tubing, ASTM F876 and CSA B137.5 require the print line, repeated at intervals of no more than 5 ft, to show the nominal size and "SDR 9", the maker's name or trademark, a production date code, the PEX material designation code, the standard numbers, pressure ratings at 73°F and 180°F, the seal of the laboratory that certified it for drinking water, and the fitting standards the maker recommends, such as F1807 or F1960.^[1]

2 PEX codes

The PEX material designation code is "PEX" plus four digits. The first digit rates resistance to hot chlorinated water, the second rates ultraviolet (UV) resistance, and the last two give the hydrostatic design stress at 73°F in hundreds of psi.^[1] A UV digit of 1, 2 or 3 means the tubing passed testing for 1, 3 or 6 months of exposure; the minimum code for drinking-water tubing is PEX 1106.^[1] In one maker's explanation, a first digit of 5 means the pipe is rated for exposure to chlorinated water at 140°F 100% of the time.^[3] Tubing color is not part of the code: red, blue and white PEX meet the same requirements, and model codes do not assign colors to hot and cold lines.^[1]

3 Copper tube

Copper tube Types K, L, M and DWV must be permanently incised with the tube type, the maker's name or trademark and the country of origin; hard (drawn) tube also has that information printed in a color that identifies the type.^[4] The colors are green for Type K, blue for Type L, red for Type M and yellow for DWV.^[4] Blue also marks ACR tube made for air conditioning and refrigeration, so the printed text matters more than the color alone.^[4] Soft (annealed) coils may carry only the incised marks. The wall-thickness differences that the colors stand for appear in the K, L and M copper entry.

4 PVC, CPVC and ABS

Plastic pressure and drain pipe is printed with the ASTM standards it meets, and some pipe is dual marked: one maker's Schedule 40 PVC carries both ASTM D1785 (pressure pipe) and ASTM D2665 (drain, waste and vent).^[2] Listing marks show the NSF standard the product was certified to: NSF/ANSI 14 for plastic piping, and NSF/ANSI 61 where the pipe is approved for drinking water.^[2] Sewer and drain pipe made only to a sewer standard is not for pressure use, and its maker warns against pressurizing it.^[2] Where markings are missing or unreadable, color and other clues described in identifying the pipes in your house help.