Compression Fittings: The Complete Guide for Plumbers and DIYers

Compression fittings have been used in UK plumbing for over a century and remain one of the most practical pipe-joining methods available. Unlike solder-ring or push-fit fittings, a compression fitting requires no heat and no specialist tool — just two spanners and the right olive. This guide covers how they work, when to choose them over the alternatives, the different types in our range, and how to avoid the mistakes that cause leaks.

How a Compression Fitting Works

A compression fitting consists of three parts: the body, a nut, and an olive (also called a ferrule). When the nut is tightened onto the body, it drives the olive against the pipe and the body's internal cone. The olive deforms slightly, biting into the pipe surface and creating a watertight mechanical seal without solder or adhesive.

This is the key advantage of compression over push-fit for permanent installations: the seal is mechanical and visible. You can inspect the nut, check the olive is seated correctly, and re-tighten if needed. On a push-fit fitting behind a wall, you are trusting the collet — on a compression fitting, you can see the joint.

Compression vs Push-Fit vs End-Feed: When to Use Each

• Compression: Use where you cannot or should not use heat (near timber, in a tight space, on live systems), for permanent joints in copper pipework, or where the joint may need to be undone again in future. Also the correct choice for connecting to old lead pipe — see below.
• Push-fit (Hep2O, JG Speedfit): Fast and demountable, excellent for first-fix where joints may need adjustment, or for plastic barrier pipe on central heating. Not a substitute for compression on high-pressure or permanently hidden joints where you want visible confirmation of seal integrity.
• End-feed / solder-ring: The strongest and most compact join — correct for completed copper runs that will be permanently hidden. Requires a blowtorch, flux, and dry pipe. Not suitable near timber without heat mats, and not for live systems.

Copper Olives vs Brass Olives

The olive is the single most important component in a compression joint. The material matters:

• Copper olives are softer, deform more easily under tightening, and are the standard choice for domestic hot and cold water pipework. Our 15mm copper olives 100-pack — £13.71 and 22mm copper olives — £0.40 each are the right choice for the majority of jobs.
• Brass olives are harder and used where vibration resistance is needed or where the fitting is in an area subject to movement — gas connections (with appropriate fittings), for example.

Do not mix olive materials with fitting bodies not rated for them. If in doubt, use copper olives on copper pipe with standard brass compression fittings.

Spare Nuts and Olives

Always keep a supply of spare nuts and olives on site — particularly if you are modifying an existing copper installation. Old olives that have been compressed cannot be reused. When you undo a compression joint, the olive is spent.

• 15mm Compression Nuts — £0.75
• 22mm Compression Nuts — £0.75
• 15mm Copper Olives, 100-pack — £13.71

Standard Compression Fittings — Straight Couplers, Elbows, and Tees

The core range covers the three basic fitting shapes in 15mm and 22mm:

Couplers (Straight Connectors)

• 8mm Compact Compression Coupler — £1.00 — for small-bore capillary connections and instrument pipework.
• 15mm × ½" FI Compression Coupler (Chrome) — £1.99 — 15mm pipe to ½" BSP female thread, chrome finish for visible pipework.
• 15mm × ½" MI Compression Coupler (Chrome) — £1.99 — 15mm pipe to ½" BSP male thread.
• 15mm Compression Coupler (Chrome) — £1.99 — inline pipe-to-pipe coupler, chrome.
• 22mm × ¾" FI Compression Coupler (Chrome) — £3.99 — for 22mm visible supply runs terminating at ¾" valves or fittings.

Elbows

• 15mm Compression Elbow (Chrome) — £2.19 — 90° direction change on 15mm, chrome for exposed runs.
• 15mm × ½" FI Compression Elbow (Chrome) — £1.99 — 90° elbow with ½" BSP female thread for tap/valve connections.
• 15mm × ½" MI Compression Elbow (Chrome) — £1.99 — male iron version.
• 22mm × 1" Female Compact Compression Elbow — £3.60

Tees

• 15mm Compression Tee (Chrome) — £3.50 — equal tee for branching 15mm runs, chrome finish.
• 15×15×1½" Compression Tee — £5.99 — 15mm run with 1½" branch outlet for cylinder/tank connections.

Wall Plate Elbows

Wall plate elbows fix to a surface and provide a threaded outlet for tap tails or valve connections. They are the standard fitting at basin and bath tap points in conventional copper installations.

• 15mm Compression Wall Plate Elbow (Chrome) — £2.99 — chrome for visible under-basin or under-bath installations.
• 15mm × ½" Compression Wall Plate Elbow (Heavy Pattern) — £2.47 — heavy pattern body for higher-pressure mains supply points.
• 22mm × ¾" Compression Wall Plate Elbow (FM) — £4.99

Tap Connectors

• 15mm × ½" Compression Bent Tap Connector — £2.79 — 90° compression fitting for connecting 15mm copper supply pipe to ½" BSP tap tails from the side.
• 15mm × ½" Compression Bent Tap Connector (Chrome) — £3.99 — chrome version for visible under-sink installations.
• 15mm × ½" Compression Straight Tap Connector — £2.99 — where the pipe approaches inline with the tap tail.

Reducing Fittings

Reducing sets allow you to connect different pipe sizes within a single compression fitting — no separate reducer needed.

• 15mm × 8mm Reducing Set — £1.25
• 15mm × 10mm Reducing Set — £1.25
• 15mm × 12mm Reducing Set — £1.25
• 15mm × ¼" Compression Adaptor — £2.99 — for connecting to ¼" BSP instruments and pressure gauges.
• 22mm × 15mm Compression Reducing Coupler — £2.25
• 22mm × 15mm Compression Reducing Coupler (Chrome) — £2.99
• 22mm × 15mm 3-piece Reducing Set — £1.50

DZR Fittings — For Mains Water and Dezincification-Risk Areas

DZR stands for dezincification-resistant. Standard brass contains around 35% zinc, which in hot mains water — particularly in hard water areas like London — can leach out over time, leaving a porous copper shell. This process, dezincification, causes fittings to fail without warning.

DZR brass contains inhibitors (typically arsenic or antimony) that prevent this process. For mains cold water supply, mains-fed hot water, and any fitting in a hard water area, DZR is the professional specification. Water regulations in hard water zones require fittings marked DZR or CR (corrosion resistant) on mains pipework.

• 15mm Double Check Valve (DZR) — £3.09 — prevents backflow on mains supply connections. Required by Water Regulations where there is a risk of back-siphonage (garden hose connections, outside taps, appliance fill loops).
• 22mm Double Check Valve (DZR) — £6.21
• 22mm × 1" Female DZR Compression Elbow — £5.98
• 22mm × ¾" Male DZR Compression Elbow — £4.70
• 15mm × ⅜" FI Compression Coupler (Heavy) — £1.99
• 22mm × ½" FI Compression Coupler (Heavy) — £2.80

42mm and 54mm Heavy Pattern — Main Supply and Commercial

Heavy pattern compression fittings in 42mm and 54mm are for main supply runs, commercial or light industrial installations, and high-flow pipework where standard fittings would be undersized.

• 42mm Compression Coupler (Heavy Pattern) — £13.50
• 54mm Compression Coupler (Heavy Pattern) — £19.99
• 42mm DZR Compression Elbow — £19.99 — DZR body for 42mm mains connections.
• 42mm × 1½" MI Compression Coupler (Heavy) — £10.99

Lead Pipe Connections

Older London properties, particularly pre-1970 housing stock, may still have sections of lead supply pipe. Connecting modern copper to lead requires a specialist fitting — a standard olive cannot grip a lead pipe reliably. These fittings use a wiped solder-joint-style lead cup one end, copper compression the other.

• ½" 7lb Lead × 25mm MDPE Compression Coupler — £13.99 — connects ½" lead supply pipe to 25mm MDPE (blue water service pipe). Standard fitting for lead pipe replacement to the boundary.
• ½" 7lb Lead × 20mm MDPE Compression Coupler — £12.26
• ¾" 11lb Lead × 25mm MDPE Compression Coupler — £19.74 — for larger ¾" lead supply mains.

Note: if you discover lead supply pipe during a renovation, current Water Industry guidance recommends replacement. These fittings are for transition joints where the supply pipe is being partially or fully replaced. Contact your water supplier before work on the section between the boundary and the meter.

Air Vent and Stop End

• Compression Air Vent Brass 15mm — £0.89 — manual air vent for compression fitting into a radiator or pipework high point.
• 15mm Compression Stop End (Chrome) — £1.99 — for capping a 15mm copper pipe end. Chrome for visible installations.
• 15mm Compression Tank Connector (Heavy Pattern) — £2.40 — for connecting pipework to a cold water storage tank or header tank, through the tank wall.

Installation Notes

How tight is tight enough?

Hand-tight, then one to one-and-a-quarter turns with a spanner. Over-tightening splits the olive and destroys the fitting. Under-tightening means the olive hasn't bitten into the pipe. For 15mm fittings on domestic water, one-and-a-quarter turns past hand-tight is the standard. On 42mm and 54mm heavy pattern, one turn is typically sufficient — the larger olive has more contact area.

Pipe preparation

Cut copper pipe square — a pipe slice gives the cleanest cut and removes the need for deburring. Deburr the pipe end to remove swarf that can damage the olive seat. Do not use PTFE tape on the olive or the fitting body — PTFE is for threaded connections, not olive seals.

Reconnecting an existing joint

If you are undoing and redoing a compression joint, always fit a new olive. A compressed olive cannot reseal reliably. Keep spare olives and nuts on site for this reason.

Quick Specification Reference

All fittings in stock at our Acton trade counter for same-day collection. If you are fitting out a full copper installation and need olives in bulk, call ahead and we'll have your order ready.

APM Plumbing & Electrical | 24 Western Avenue, Acton, London W3 7TZ | 020 8702 8080 | apmi.uk