The fittings on American machines arrive as a family group rather than one at a time. American-built machines — and machines built anywhere for the North American market — bring the inch families with them, and they arrive as a group rather than one at a time. A workshop whose fleet has been metric and BSP until now meets four new things in one afternoon, two of which look enough alike to be swapped.
The four, and what each seals on.
| Family | Where it seals | Thread |
|---|---|---|
| JIC 37° flare | A 37° cone, metal to metal | Straight, inch |
| ORFS | A flat face, on an O-ring set into it | Straight, inch |
| NPT | On the thread itself, as it wedges | Tapered, inch |
| SAE O-ring boss | An O-ring under the shoulder, against the port face | Straight, inch |
The two straight-threaded ones are the pair worth learning by sight. A JIC male is a plain cone; an ORFS male is a flat face with a groove and an O-ring in it. Once you have looked at both, you will not confuse them again — but until you have, the hex sizes and the general shape are similar enough to invite it.
The mistake that costs a port.
The reverse case is quieter and just as common: a straight male in a tapered port, which never seals properly and gets tightened harder in the hope that it will. Taper and straight is the first thing to establish, before size and before family — run a straight edge along the thread, or start a nut on it and see whether it runs freely down the length.
What a metric workshop should add.
Adding a second family properly beats adapting between families badly. For a workshop taking on one or two American machines, the useful additions are JIC ends in the bores those machines actually use, ORFS if the machine has it, a small set of O-ring boss plugs and studs, and the bridging adapters between JIC and whatever your existing fleet is. Do not try to cover the inch world with adapters stacked on metric parts — that is three leak paths where there should be one.
JIC adapters
37° flare adapters, unions and bridging parts.
ORFS adapters
Flat-face O-ring adapters and O-ring kits.
Can a JIC fitting go into an ORFS port?
No. One seals on a cone and the other on a flat face with an O-ring, so even where a thread engages there is no sealing geometry. Use the correct family, or a proper adapter between them.
Is PTFE tape correct on these fittings?
On NPT, where the thread itself seals, a thread sealant is normal — applied so that it cannot enter the system. On JIC, ORFS and O-ring boss it is wrong: the seal is made at the cone, the face or the O-ring, and tape on the thread only masks a joint that is not seating.
How do I tell a tapered thread from a straight one quickly?
Start a matching nut or look along the crests against a straight edge. A taper narrows visibly over the length of the thread; a straight thread does not. It takes seconds and it prevents the expensive mistake.
Adding an imported machine to a metric fleet?
Send photographs of the ports and hose ends. We will tell you which families the machine actually carries, what to add to the drawer, and which bridging adapters are worth having — as one quotation rather than five parcels.
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