Straight Joint, Brass

Quick Answer: The Straight Joint, Brass is an in-line brass pipe fitting, also called a coupling or socket, that joins two lengths of pipe end to end in the same direction, used to extend or repair the water and gas service lines that supply laboratory benches.

Joining Two Pipes in Line

Service pipes come in fixed lengths, and a run along a bench spine or across a ceiling often needs more than one. The brass straight joint connects them without changing direction, so the pipe carries straight on. It is also the usual repair fitting: a damaged section is cut out and replaced with a short new piece, joined at each end by a straight joint.

Straight joints are made in several end patterns. A female-to-female coupling screws onto two male-threaded pipe ends; a male-to-female version joins a pipe to a fitting; a reducing coupling steps from one pipe size to another; and compression couplings grip plain copper tube with a nut and olive. The listing does not state which pattern or size this is, so the pipe material, outside diameter and thread standard should be matched before ordering.

Brass is used because it machines to accurate threads and stands up to most mains water without rusting. On gas lines, only fittings and sealants suited to gas should be used, and the joint must be made and leak-tested by a qualified fitter. Where the run must turn a corner, the brass elbow L joint does that job, and the brass T-joint takes off a branch.

Specifications

Installation Notes

• Cut pipe ends square and remove burrs so they seat fully in the coupling.
• Wind PTFE tape clockwise as seen from the thread end, two or three turns, keeping it off the first thread.
• Tighten with two spanners, one holding the coupling, and do not overtighten brass threads.
• Pressure or leak test the joint before closing up any panel.

Applications

• Extending water supply lines along a bench service spine.
• Repairing a damaged section of pipe by splicing in a new length.
• Joining gas pipework runs to bench taps, where the fitting is suited to gas.
• Connecting a pipe to a valve or tap tail with a male-female coupling.

Why Choose LabEquip

Plumbing contractors, lab furniture fitters and estates teams buy brass straight joints by the box for installation and repair work. LabEquip lists them in General Lab Products with the other brass fittings; a note of the pipe diameter and whether threaded or compression ends are needed can be sent via the contact page.

Frequently Asked Questions

What is a straight joint in plumbing?

It is a fitting that joins two pipes end to end in a straight line, also known as a coupling or socket. It neither changes direction nor splits the flow.

How is a straight joint different from a union?

A straight coupling is one piece, so a pipe cannot be removed without unscrewing a whole run. A union has a separate nut that lets the joint be taken apart, which is useful beside valves or equipment that may need removal.

Can a brass straight joint be used on gas lines?

Brass is a common material for gas couplings, but only couplings and sealants rated for gas should be used there, and the work must be carried out and leak-tested by a qualified gas fitter.

Which sealant should be used on the threads?

PTFE tape or a thread sealing compound suited to the service. For drinking water, use a product approved for potable water, and for gas, a tape or compound approved for gas.

Why does brass sometimes corrode in water lines?

In some soft or aggressive waters, ordinary brass can slowly lose its zinc, a process called dezincification, which leaves a weak, porous fitting. Dezincification-resistant brass is specified where this is a known problem.

Can it join pipes of different sizes?

Only a reducing coupling can do that; a standard straight joint has equal ends. If two sizes meet, order the reducing pattern and state both sizes.

Last Updated: September 2026