How to connect PEX, copper, PVC and galvanized pipe
Two kinds of pipe join through a fitting made for both. Copper, PEX and the CPVC used for house water lines share one size system, so one push-to-connect coupling joins any two of them.
Flexible plastic, often white, red or blue
Copper-colored metal, soldered or pressed joints
What fits
A push-to-connect coupling, or a brass PEX x copper adapter
On the package: Push-to-connect coupling in your pipe’s size, e.g. 1/2 in.
PEX is made to copper tube size, so 1/2" PEX and 1/2" copper are both 5/8" across
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Shut the water off and drain the line before you cut anything.
No soldering: standard push-to-connect fittings (SharkBite’s tan collar) take copper and PEX in any combination, with the PEX stiffener built in. Cut each pipe square, deburr it, mark the insertion depth and push it in to the mark.
Soldered: a brass adapter with a copper end on one side and a PEX end on the other. Solder the copper side first, then the PEX joint, using an adapter made for your kind of PEX joint.
Uponor’s instructions keep solder and flame at least 18" from the PEX on the same line. Uponor also makes copper press adapters, which join with no flame at all.
The sizes match, but PEX joins with rings or fittings and copper usually with solder, so use a transition fitting.
Galvanized steel needs a threaded fitting, and to copper the codes call for a dielectric union or a brass fitting. PVC is iron pipe size, wider than copper, PEX or house CPVC of the same size name, so it takes a transition coupling.
Water pipe uses two size systems. In both, the size on the label isn’t the pipe’s width. A fitting from one system doesn’t fit pipe from the other, even with the same size on the label.
Which size system each pipe uses
Pipe
Size system
1/2" pipe across
Usual joints
Copper
Copper tube size (CTS)
0.625" (5/8")
Solder, press, compression, push-to-connect
PEX
Copper tube size
0.625"
Rings, crimps or expansion fittings, push-to-connect
CPVC (house water lines)
Copper tube size
0.625"
Glue, push-to-connect
PVC
Iron pipe size (IPS)
0.840"
Glue
Galvanized steel
Iron pipe size
0.840" across the threads
Pipe thread
What the code requires
The plumbing codes require a joint between two pipe materials to be made with a fitting meant for it: a compression or mechanical joint with a rubber seal, or an approved adapter or transition fitting. Between copper and galvanized steel they’re specific: a brass fitting, a dielectric fitting, or (in the IPC) a dielectric union listed to ASSE 1079, screwed onto the steel with the copper joined to its other side.
Threads between plastic and metal
Plastic male into metal female works, but a plastic male adapter is for cold water only.
Metal male into plastic female puts heavy stress on the plastic and isn’t recommended. Use a female metal fitting instead.
For hot water on CPVC, use a CPVC x brass threaded transition fitting, so metal threads meet metal.
Tighten plastic threads with a strap wrench, two turns past finger tight at most.
Heat near plastic pipe
Make every solder joint before the PEX joints. Uponor’s instructions keep soldering at least 18" away from its PEX on the same water line. Press and push-to-connect fittings need no flame.
These fittings are for water lines. Never use them on gas pipe: gas connections are a job for a licensed pro.
No. SharkBite's own instructions rule out galvanized pipe for its push-to-connect fittings. Use a threaded fitting on the steel, and change to copper or PEX after it.
Do I need a dielectric union between copper and galvanized pipe?
Not always a union. The codes name a brass fitting, a dielectric fitting or (IPC) a dielectric union for this joint.
Can PEX connect directly to PVC?
Not with ordinary fittings, because PVC is wider than PEX of the same size name. A CTS x PVC transition coupling joins PEX to PVC.
The sizes on this page come from published standards and the makers’ own documents. Checked against published data from SharkBite, Uponor, Copper Development Association, Charlotte Pipe and International Code Council (plus 5 more).
See all 19 sources
National Bureau of Standards, Handbook H28 (1957) Part II: Table VII.2 (American Standard taper pipe threads, NPT) and Tables X.1–X.3 (hose coupling threads, NH)
Copper Development Association, Copper Tube Handbook (ASTM B88 tube dimensions)
Uponor, Plumbing Design Assistance Manual (PEX is copper tube size)
JM Eagle, PVC Schedule 40/80 submittal (ASTM D1785 outside diameters)
Swagelok, Thread Sealants catalog (MS-14-01): PTFE tape, how to apply
Reliance Worldwide, SharkBite PVC Fittings Sales & Specifications Sheet (2015): white collar fits Schedule 40, 80 and 120 PVC
SharkBite (Reliance Worldwide), SharkBite PEX Installation Guide (2021): fits copper, CTS CPVC and PEX in any combination
Copper Development Association, The Copper Tube Handbook (2026): identification, color codes, joining
Uponor, PEX Piping Systems Installation Guide, seventh edition (2025): ProPEX expansion fittings, pipe colors, copper and threaded adapters, no soldering within 18" of PEX
Uponor, PEX-a Installation Guide, second edition (2024): ASTM F876/F877, red and blue pipe (copy on a retailer server)
Charlotte Pipe, Plastics Technical Manual (2026): PVC and CPVC colors, standards, temperature limits, Not for Pressure print, plastic-to-metal threads and brass transition fittings
Charlotte Pipe, FlowGuard Gold CTS CPVC submittal and product page: ASTM D2846, 180 F, solvent cement
Michigan Administrative Code R 408.30727 and R 408.30729: Tables 605.4 (water distribution) and 605.3 (water service pipe)
International Plumbing Code 2021, sections 605.23, 605.23.1 and 605.23.2: joints between different materials, copper to galvanized steel (as adopted in South Carolina)
International Residential Code 2021, sections P2906.18 and P2906.18.1-P2906.18.3: joints between different materials, PVC service to CPVC (as adopted in South Carolina)
General guidance from manufacturer and standards data. Parts vary by brand, so check the size printed on the package against what you measured. For gas lines or anything inside a wall, use a licensed plumber.