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Choosing the wrong thread is the most common reason a pneumatic quick-connect fitting leaks or fails to assemble. The same nominal size can exist in several standards with different pitches, flank angles and sealing principles, so it pays to identify the thread before ordering. Below is a summary of the standards used on AFD metal quick-connect fittings.

Parallel (straight) threads

Parallel threads hold pressure through a face seal or an O-ring, not through the thread flanks. The common families are:

• BSPP (G, British Standard Pipe Parallel) — 55° flank angle, ISO 228. Sealed by a bonded washer or O-ring.
• UNF / UNS / UN / UNEF (Unified) — 60° flank angle, inch sizes with fine, special, constant and extra-fine pitches.
• NPSM — American National straight mechanical pipe thread, 60°.
• NH — American National hose-coupling thread for fire equipment.
• Metric parallel (M) — designated by outer diameter and pitch, e.g. M5×0.8, M10×1.0.

Taper threads

Taper threads seal on the flanks as they are tightened, usually with a thread sealant; the taper drives the flanks together.

• NPT / NPTF (American National Taper Pipe) — 60° flank angle, NPTF (dryseal) deforms the crests to fill clearances.
• BSPT (R, PT, ZG) — 55° flank angle, ISO 7, taper equivalent of BSPP.

Reference dimensions — parallel threads

Reference dimensions — taper threads

Practical selection notes

A 1/2-14 NPT male will thread into a 1/2-14 NPSM female for a low-pressure mechanical joint, but never confuse a 1/2-14 BSPP with a 1/2-14 NPT: the pitches differ (1.814 mm on both, but flank angles are 55° vs 60° and diameters differ) and forcing them together ruins both threads. On AFD fittings, R-designated studs are BSPT, G studs are BSPP, and NPT is called out explicitly. Metric studs are marked M-OD, e.g. PC6-M10 accepts 6 mm tube onto an M10×1.0 stud.

If you are unsure which thread a mating port has, measure the outside diameter and count turns per inch, or send a sample to us — AFD Pneumatic supplies fittings in R, G, NPT and metric studs from M5 to 1/2 in, and we will match the thread from a photo or sample.

Stainless steel quick-connect fittings are the push-in solution for gas lines where corrosion, wash-down or temperature would degrade plated brass. This guide summarises the realistic working envelope and the applications where they earn their premium.

Typical working envelope

Where they excel

• Corrosive atmospheres — chemical processing lines, coastal or marine equipment, plating and wash-down areas where plated brass would pit. 316L is the default for chloride exposure.
• Hot water and low-pressure steam-adjacent lines — well above the +60 °C comfort limit of standard nylon-tube brass assemblies, within the seal limits above.
• Food, beverage and pharma wash-down zones — stainless survives caustic CIP cycles; note that compliance certificates must be requested per order.
• Vibrating equipment — the gripping collet and O-ring keep the tube locked where barbed fittings walk out.

Compatible media

Within the stated envelope: compressed air, inert gases, potable and sea water, hot/cold water, fuels and lubricating oils. Media beyond these — strong acids or alkalis, solvents, live steam above 110 °C — depend on the seal material as much as the body, so the medium, concentration, temperature and tube material should be confirmed with the manufacturer before use.

Limitations to check before ordering

• Seal and tube chemical resistance is separate from body corrosion resistance — confirm both.
• Potable-water or food-contact use requires the relevant certificates; ask for them explicitly.
• Where catalogue text and the datasheet disagree (e.g. occasional steam claims above the +110 °C rating), treat the datasheet as binding.

Quick answers

Can stainless quick fittings handle corrosive chemical lines? 304/316/316L bodies are specified for exactly that class of environment; final compatibility depends on concentration, temperature and seals — send us the medium for confirmation.

Stainless or nickel-plated brass? Plated brass wins on cost for dry compressed air; stainless wins wherever plating would be attacked, washed down, or where contamination from corrosion matters.

AFD Pneumatic manufactures 304/316 stainless quick-connect fittings with G, R, NPT and Rc threads — send us your operating parameters and we will confirm the right series.