A brass fitting spec sheet packs a lot into a short product line: an alloy grade, a thread callout, and a pressure rating, often abbreviated to the point of being unreadable if you don't work with fittings every day. Getting any one of the three wrong doesn't usually show up until the fitting is already installed — a thread that won't seal, a fitting that corrodes faster than expected, or one rated for less pressure than the line actually runs. Here's what each part of the spec actually tells you.
The alloy grade: what "brass" alone doesn't tell you
"Brass" is a family of copper-zinc alloys, not one material, and the specific alloy affects strength, machinability and corrosion resistance. Free-cutting brass alloys are commonly used for fittings that are machined in volume, valued for how cleanly they cut on high-speed machinery. Where a fitting will sit in continuous contact with water — potable water lines, underground fittings, or anywhere a slow corrosion process called dezincification is a risk — a dezincification-resistant (DZR) brass alloy is the safer specification, since standard brass can lose zinc from its surface over time in certain water chemistries and weaken as a result.
If your spec sheet or supplier doesn't state the alloy, or simply says "brass," ask. For a fitting in permanent water contact or a corrosive environment, that one line item is worth confirming before you commit to a quantity.
The thread callout: BSP, NPT, and why they aren't interchangeable
Thread standard is the single most common source of a fitting that "should" work but doesn't seal. BSP (British Standard Pipe) and NPT (National Pipe Taper) are the two standards you'll see most often on brass fittings sold internationally, and they are built differently:
| Thread Standard | Form | How it seals |
|---|---|---|
| BSPP (parallel BSP) | Straight, non-tapered | Bonded seal — washer, O-ring or sealing face |
| BSPT (tapered BSP) | Tapered | Thread engagement, often with sealant/tape |
| NPT | Tapered | Thread engagement, sealant/tape recommended |
BSPT and NPT use different thread angles and pitch, so a fitting cut to one will often start threading onto the other and then bind or leak once tightened — it can look like a fit for the first couple of turns before the mismatch shows. Always confirm which standard your existing pipework or equipment uses before ordering a replacement or matching fitting; this is the same principle we flag on our own valves and taps listings, where we ask buyers to confirm BSP or NPT before ordering since the two aren't interchangeable without an adapter.
The pressure rating: PN, and why temperature matters too
Pressure ratings on brass fittings, valves and flanges are commonly expressed using the PN ("pressure nominal") system — a number such as PN16 or PN25 that denotes the maximum working pressure in bar at a defined reference temperature. The number alone isn't the whole picture: allowable working pressure for a given fitting typically drops as operating temperature rises, so a fitting rated PN16 at room temperature will not necessarily hold that rating in a hot-water or steam line. Always check the rated pressure against your actual operating temperature, not just the cold rating printed on the spec sheet.
Buyer's rule of thumb: a complete brass fitting specification has three parts that must all be confirmed together — alloy grade (and DZR status if the application involves water), thread standard (BSPP, BSPT or NPT, matched to your existing pipework), and pressure rating (checked against your actual operating temperature, not just the label). Confirming all three in writing before an order is placed is the single biggest step toward avoiding a fitting that doesn't perform as expected.
Specifying for export orders
For cross-border orders, confirm the alloy grade, thread standard and pressure rating in writing at enquiry stage rather than assuming from a general product description — the same specification-confirmation step we apply to every order before production or sourcing begins. Where a fitting requires supporting documentation for customs or the buyer's own quality process, ask what's available for that specific product before you commit.
Specifying brass fittings for an order?
Send your alloy, thread standard and pressure requirement and we'll confirm what we can supply before you commit.