John Guest tube expander
Adapter to go from a smaller‑diameter plain spigot to a push‑fit connection for larger‑diameter tube. Current variants include 5/16" plain spigot to 3/8" tube and 3/8" plain spigot to 1/2" tube.
What it’s for
Allows you to increase the line diameter in a compact transition, avoiding the need to combine several fittings when the installation has a plain spigot outlet.
How to choose the variant
First identify the size of the existing plain spigot and then the outside diameter of the tube that will continue the line. Both values must match the variant.
Installation
Depressurize, check that the tailpiece is clean and in good condition, install the adapter and prepare the tube with a perpendicular cut before inserting it fully to the stop.
Use and maintenance
Avoid using the extender to correct misalignment or to keep the tube under continuous bending. At each service, check retention and leak tightness.
Frequently asked questions
Does it reduce or increase the diameter?
These variants are designed to go from a smaller tailpiece to a larger-diameter tube.
What combinations are available?
5/16" to 3/8" and 3/8" to 1/2".
Are the barb and the tube the same connection?
No; each side serves a different function.
What mistake should I avoid?
Confusing the spigot size with the tube’s outside diameter.
