Male Straight Adapter 8 mm Tube x 3/8" BSPT, ref. AAMC0806M

Straight adapter 8 mm × 3/8" BSPT

Straight fitting connecting 8 mm semi-rigid tubing to a 3/8" BSP female thread. On the tube side, a push-fit connection: the tube is pushed fully home, the collet locks it and the O-ring seals it. On the thread side, a 3/8" BSPT male.

8 mm tubing

8 mm is a metric diameter, not to be confused with the imperial sizes of the Anglo-Saxon market.

It sits between 6 mm and 10 mm and comes close to imperial 5/16" without being identical to it. It is an intermediate size, useful where 6 mm restricts flow too much and 10 mm takes up too much room.

Watch out. 8 mm tubing fits only a fitting designed for 8 mm. Metric tubing in an imperial fitting, or the reverse, is not gripped correctly by the collet and leaks under pressure. Always check the standard of your tubing before ordering: it is the most common mistake on quick-connect fittings.

BSPT: a tapered thread

BSPT (British Standard Pipe Taper, ISO 7/1) is a tapered thread. Unlike a parallel thread that seals on a flat face or a gasket, BSPT seals on the threads themselves: the taper wedges into the port and tightening creates the contact.

Two practical consequences.

Sealant is always required, PTFE tape or pipe sealant, applied in the direction of tightening.

And do not overtighten: on a polymer port the taper acts as a wedge and can split the receiving thread. Hand-tight plus a quarter turn with a spanner is enough in most cases.

Do not confuse with NPTF

BSPT is the European standard, NPTF the American one. Both are tapered, but thread angle and pitch differ, 55° against 60°. They are not interchangeable: a BSPT male in an NPTF port engages only a few threads and will eventually leak or strip.

Always check the standard of the receiving port before ordering.

Where to use it

On reverse osmosis systems and water treatment installations using metric tubing, to connect an 8 mm line to a 3/8" BSP threaded port: valves, solenoid valves, pressure gauges, pump bodies, filter heads.

Fitting

Thread side: apply PTFE in the direction of tightening, screw in by hand, finish with a quarter turn.

Tube side: cut square and clean, an angled or crushed cut compromises the O-ring seal. Push in until it bottoms out, then pull lightly to check engagement. To disconnect: shut off the water, depressurise, push the collet towards the fitting body and pull the tube out.