AN T-Pieces, Y-Pieces, Reducers

T-pieces, Y-pieces and reducers split a line, join two lines or change its size. In a fuel system they feed two rails from one supply, add a gauge or sensor, merge returns, or step between AN sizes. This category covers fittings in aluminium, stainless steel, brass and white plastic, for AN and pipe threads and for push-on hose.

Flow area governs how they behave, because the trunk must feed every branch at once. In a Y adapter such as AN6-AN6-AN8, the two AN6 branches together offer at least the flow area of one AN8. A Y also splits the stream at a shallow angle, with less turbulence than a T.

With reducers, the smallest bore limits the whole line, so a size change belongs at the component that needs it, not halfway along a run. Every extra joint adds a little pressure drop and one more place to leak.

Choose the shape, then the threads:

• T-pieces: aluminium AN tees from AN3 to AN16 and stainless AN3 tees for small hydraulic lines. Bulkhead tees branch a line where it passes a panel.
• Swivel tees: nut on the side branch in AN6, AN8 and AN12, or in the run in AN8, so the tee can be turned before tightening.
• Y adapters: male AN6-AN6-AN6, AN6-AN6-AN8, AN8-AN8-AN8 and AN8-AN8-AN10, and a forged Y block with three 1/2 NPT female ports and an extra 1/8 NPT port.
• Expanders: female to male, in steps from AN3-AN4 up to AN10-AN16.
• Pipe and sensor tees: female NPT couplers from 1/8 to 1 NPT. Sensor tees, M10×1 or M16×1.5 male to 1/8 NPT female, let an extra sender share one engine port.
• Plastic and brass: white nylon or POM tees and Y-pieces, and brass tees, listed by size from 3 to 25 mm, including reducing 8-4-8 mm types. They suit vacuum, breather and low-pressure push-on hose, clamped and clear of exhaust heat.

A tee with three hoses carries their weight and vibration, so clamp it to a bracket or use a bulkhead tee. Rigid tees cannot be turned once tight, so assemble loosely, align, then tighten each joint while holding the tee body. Seal NPT male threads with a fuel-resistant compound, leaving the first thread clean, and never force a taper deep into aluminium, which can split the port. Pressure test any changed fuel or oil circuit and watch each new joint, especially a gauge or sensor branch.