What the standard pins down
ISO 7-1 specifies pipe threads intended to make a pressure-tight joint on the threads themselves. Its designations are R for a tapered external thread, Rp for a parallel internal thread meant to receive one, and Rc for a tapered internal thread.
Where the parallel family relies on a washer, this one relies on interference: a tapered male entering a mating female wedges as it goes, and the flanks deform slightly against one another until the joint holds. The document fixes the taper, the profile, the pitch for each designated size, the gauge lengths and the tolerances that make that interference repeatable rather than a matter of how hard you pulled.
It shares the inch-based size names with the parallel family, and it shares them exactly: an R 1 and a G 1 are the same nominal size with different behaviour. That is a convenience for manufacturing and a trap for buyers.
What it does not promise
It does not promise a dry joint without a sealant. In practice a tapered joint on domestic equipment is made with tape or a jointing compound, and the standard’s tolerances allow for it rather than requiring the metal alone to do the work.
It does not promise that a joint can be broken and remade indefinitely. Each assembly deforms the flanks a little more, and a fitting that has been on and off a pump port several times seals less well each time.
It does not tell you which family your pump has. A port marked only with an inch size has told you the size and nothing about the family — and on the imported end of the pump shelf that is the usual state of the marking.
It does not promise a bore. As with the parallel family, the inch designation is a legacy size name and not a diameter you can measure or a flow you can expect.
The documents it sits next to
The parallel family is the sibling document, and the two are read together: almost every failure in this area is a pairing question rather than a manufacturing one.
The pump behind the port has its own appliance standard. The hose on the other side of the fitting has its own document for bore and reinforcement.
Which shelves it reaches here
The pump family cites it, because that is where the tapered ports are. The connector, sprinkler and rain barrel families cite it because the brass end of those shelves mixes the two families freely and the listings rarely say which is which.
Where a product page here can name the thread family, it does. Where the maker states only an inch size, the page prints the inch size and says the family is unstated, rather than assuming the one that is more common. On this shelf the assumption would be wrong often enough to matter.
The questions that keep coming in
How do I tell a tapered thread from a parallel one?
By eye at the end: a tapered male thread is visibly shallower at the tip than at its base, and the first turn or two goes on easily before it tightens. A parallel one engages the same all the way. On a female port the difference is harder to see, which is why the marking on the pump body matters.
Do I need PTFE tape on a tapered thread?
The family is designed to seal on the threads, and a sealant or tape is the normal way to make that joint reliable in practice. On a parallel thread with a washer it achieves nothing and can prevent the faces meeting.
My pump port is Rp 1in and my fitting is G 1in. Will it work?
A parallel male into a parallel-designated female is the intended pairing for that combination, and it is the one a pump with an Rp port expects. What does not work reliably is forcing a tapered male into a fitting made for a washer face, or the reverse.
Last reviewed 26 September 2026