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How to Tell Copper Tube from Copper Pipe and ACR

Plumbing copper tube, ACR tube and copper pipe use different size systems. This sheet shows how to tell them apart by outside diameter and markings so the right fittings are ordered.

Ref PV-0067ASTM B88ASTM B280ASTM B42

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Three copper products look alike but are sized differently.

Copper water tube (ASTM B88), Types K, L and M. Sized by nominal size. The outside diameter is always 1/8 in. larger than the nominal size. A 1/2 in. Type L tube has a 5/8 in. (0.625 in.) OD.
ACR tube (ASTM B280) for air conditioning and refrigeration. Sized by actual outside diameter. A 5/8 in. ACR tube has a 0.625 in. OD. It is cleaned and capped to keep it dry and clean inside.
Copper pipe (ASTM B42), seamless copper pipe in iron pipe size (IPS). Its OD matches steel pipe of the same nominal size, so it can be threaded. A 1/2 in. copper pipe has a 0.840 in. OD.

How to identify

Measure the outside diameter with a caliper.
Read the marking. Type K, L and M tube is printed or stamped with type, maker and country of origin. ACR tube is marked ACR. B42 pipe names the standard.
Check the stripe color on hard-drawn water tube. See Copper Tube Type Color Code Chart.
Check the ends. ACR tube is sold with caps or plugs and is often charged with nitrogen.
Check the use. Refrigerant lines use ACR. Domestic water uses K, L or M.

Size comparison

Product	Standard	Sized by	Example name	Example OD
Water tube Type K, L, M	ASTM B88	Nominal size, OD = nominal + 1/8 in.	1/2 in. Type L	0.625 in.
ACR tube	ASTM B280	Actual OD	5/8 in. ACR	0.625 in.
Copper pipe (IPS)	ASTM B42	Nominal pipe size, OD = steel pipe OD	1/2 in. copper pipe	0.840 in.
DWV tube	ASTM B306	Nominal size, OD = nominal + 1/8 in.	1-1/2 in. DWV	1.625 in.

The 1/2 in. Type L tube and the 5/8 in. ACR tube in the table have the same OD. They are named differently because they follow different standards.

Key points

Fittings for water tube are named by nominal size. ACR fittings are named by OD. A 1/2 in. sweat fitting fits 5/8 in. ACR tube.
Wall thickness differs between K, L, M and ACR. See Copper Tube Types K, L, M and DWV.
Copper pipe to B42 is a different, heavier product. It does not fit sweat fittings for tube.
See ACR Tube Size Chart — Actual OD vs Plumbing Nominal.

Common mistakes

Ordering 5/8 in. fittings for 1/2 in. water tube.
Using plumbing tube for refrigerant lines.
Calling all copper "pipe."
Guessing type by color stripe when the stripe is missing.

Governing standards: ASTM B88 (seamless copper water tube); ASTM B280 (seamless copper tube for ACR field service); ASTM B42 (seamless copper pipe, standard sizes); ASTM B306 (copper drainage tube).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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