Pipe Wrenches (Stillsons): How They Work and Which Size to Buy
The UK guide to pipe wrenches. How the self-tightening jaw works, which size you need, the two-wrench technique, and what to buy from £10-40.
Your plumber arrives to connect the new boiler. He reaches for a heavy wrench with serrated jaws, grips the old iron gas pipe, and breaks the corroded fitting free in one turn. That tool is a pipe wrench. If you'd attempted the same job with an adjustable wrench, the smooth jaws would have slipped on the round pipe, scarred your knuckles on the wall behind, and left the fitting exactly where it was. A pipe wrench is the only hand tool that reliably grips round pipe. Without one, you can't disconnect or reconnect threaded pipe fittings, and that's a job that comes up repeatedly during any extension or renovation.
What it is and when you need one
A pipe wrench is a large, heavy wrench with two sets of serrated teeth: one on the fixed lower jaw (called the heel jaw) and one on the upper jaw (the hook jaw) that pivots on a pin. You turn a knurled adjusting nut to open or close the jaws around the pipe. The clever part is what happens when you pull the handle. The hook jaw is mounted at a slight angle, so as you apply turning force, the jaw cams inward and the teeth bite deeper into the pipe surface. The harder you pull, the tighter it grips. Release the force and the jaw relaxes.
This self-tightening mechanism is what separates a pipe wrench from every other wrench. An adjustable wrench relies on jaw width alone to grip flat surfaces. A pipe wrench actively digs in. That's why it works on round, smooth, corroded, or painted surfaces where nothing else will.
In the UK, plumbers and builders almost universally call these "Stillsons" regardless of who made them. The name has genericised the same way "Hoover" has for vacuum cleaners. Daniel Stillson, a machinist at J.J. Walworth Company in Cambridge, Massachusetts, carved a wooden prototype with opposing serrated teeth and filed a patent in 1869 (granted 1870). The design hasn't fundamentally changed since. If your plumber asks you to "pass the Stillsons," this is what they mean.
You need a pipe wrench for threaded iron and steel pipe connections (gas pipe, old water mains, radiator tails), stubborn waste fittings that have seized with age, and any situation where you're gripping a round surface that an adjustable wrench can't hold. During second-fix plumbing on an extension, that means boiler connections, waste trap assemblies, bath and shower mixer tails, and connecting into existing pipework.
Types and sizes
Pipe wrenches come in one basic pattern (the Stillson pattern) but in a range of sizes. The size that matters is the overall length, because length determines both jaw capacity and the turning force you can apply.
| Size | Jaw capacity | Weight (steel) | Best for |
|---|---|---|---|
| 10" (250mm) | ~38mm / 1.5" | ~1kg | Tight spaces under sinks, small-bore pipe (15-22mm copper), confined access |
| 12" (300mm) | ~42mm / 1.6" | ~1.3kg | General domestic plumbing, 15-28mm pipe, good all-rounder for light work |
| 14" (350mm) | ~50mm / 2" | ~1.8kg | The most versatile size. Handles waste pipe fittings (40-50mm), radiator tails, boiler connections. Buy this one first. |
| 18" (450mm) | ~64mm / 2.5" | ~2.7kg | Larger waste connections, external stop valves, stubborn fittings that need serious turning force |
| 24" (600mm) | ~76mm / 3" | ~4kg | Professional/commercial. Too heavy and unwieldy for most domestic work |
For a home extension project, a 14-inch pipe wrench handles 90% of residential plumbing tasks. The jaw opens wide enough for 40mm and 50mm waste fittings, and the handle is long enough to break corroded threads without excessive force. If you're buying one wrench, buy a 14-inch.
If you can justify a second, add a 10-inch or 12-inch. The smaller wrench acts as your backup (holding the pipe while the 14-inch turns the fitting) and fits into the cramped spaces under sinks and behind toilets where a 14-inch won't.
Steel vs aluminium
Traditional pipe wrenches are cast iron and steel. They're heavy but indestructible. Aluminium-handled versions weigh up to 40% less, which matters if you're working overhead or holding the wrench at arm's length for extended periods. For a homeowner who'll use it a handful of times, the weight difference doesn't justify the higher price. Steel is fine.
How to use it properly
Setting the jaw gap
This is the detail that trips up beginners. The jaws should not clamp tight onto the pipe before you start turning.
Open the jaws with the adjusting nut until the pipe slides in with about a 3mm (1/8 inch) gap between the back of the hook jaw and the pipe surface. That gap is what allows the cam action to work. When you pull the handle, the hook jaw rocks forward and closes that gap by biting into the pipe. If you start with zero gap (jaws clamped tight), the cam action has nowhere to go and the wrench won't grip properly.
Direction matters
A pipe wrench only grips in one direction. The teeth are angled so they bite when you pull the handle toward you (or push it away, depending on your orientation). Try to turn the wrench the other way and the teeth slide across the pipe surface without gripping.
Look at the teeth on the hook jaw. They angle toward the handle. Pull in the direction the teeth point. If you need to tighten instead of loosen, flip the wrench over so the hook jaw faces the opposite side, or reposition it on the fitting from the other direction.
The two-wrench technique
One wrench turns the fitting. The second wrench holds the pipe still.
Without a backup wrench, the torque you apply to the fitting also rotates the pipe. On a threaded connection, this can unscrew the joint at the other end of the pipe run, snap an old corroded pipe at a weak point, or twist soldered joints until they crack and leak.
Position the backup wrench on the pipe itself, facing the opposite direction to the working wrench. The two handles should point roughly apart from each other. Grip both handles and squeeze them together: one turns the fitting, the other resists. This is standard practice for every professional plumber and the reason the brief says "buy two, not one."
If you only own one pipe wrench, you can use a large adjustable wrench as the backup on fittings that have a hex section (many transition fittings do). But for pipe-to-pipe threaded connections where both surfaces are round, you need two pipe wrenches. Borrow the second one if you have to.
Thread direction
Almost all plumbing threads are right-hand (standard). Turn anticlockwise to loosen, clockwise to tighten. The exception is gas connections on left-hand threaded fittings (marked with a notch on the hex nut), but you're unlikely to encounter these on domestic work, and gas connections should be made by a Gas Safe registered engineer.
Sealing threads
Threaded pipe connections need PTFE tape on the male thread before assembly. The pipe wrench provides the mechanical tightening force; the PTFE provides the seal. Without tape, the joint weeps. Wrap the tape clockwise around the male thread (looking at the end of the pipe), so it doesn't unwind as you screw the fitting on.
Tighten threaded fittings until snug, then one to two turns past hand-tight. Stop. Over-tightening strips threads on iron pipe and cracks brass fittings. If a joint leaks after testing, give it another quarter turn before assuming it needs dismantling. Brute force breaks things.
What not to use it on
The serrated jaws are designed to bite into iron and steel pipe. They will damage anything softer or anything with a finished surface.
Never use a pipe wrench on chrome-plated taps, polished brass fittings, copper pipe, or plastic waste pipe. The teeth will score chrome permanently, crush thin-walled copper, and create stress cracks in plastic that fail weeks later under pressure. For chrome or brass fittings, use an adjustable wrench. For plastic, hand-tighten only, or use a strap wrench if more force is genuinely needed.
This is the single most common beginner mistake with pipe wrenches. The tool is brutal by design. That's its job on iron and steel. On anything else, it's destructive.
What to buy
Budget: £10-20
Own-brand and entry-level wrenches from the major retailers.
| Product | Size | Jaw capacity | Notes |
|---|---|---|---|
| Magnusson (Screwfix) | 12-inch | 42mm | Chrome vanadium steel head. Solid budget pick. |
| Forge Steel 3-piece set (Screwfix) | 12" + 16" + 20" | Various | Cheapest way to get a pair for the two-wrench technique, with a spare for stubborn fittings. |
| Draper Expert (trade suppliers) | 10-inch / 250mm | ~38mm | Drop-forged, induction-hardened jaws. Good quality, smaller size limits grip range. |
Budget wrenches work for occasional use. The jaw mechanism on cheaper tools has more play in the adjusting nut, so the hook jaw doesn't cam as aggressively and you need more force to get the same grip. For a homeowner tackling one project, that's acceptable. For daily use, it's not.
Mid-range: £25-40
This is where the serious options sit. Two stand out for UK buyers.
Two stand out:
| Product | Size | Jaw capacity | Notes |
|---|---|---|---|
| Magnusson (Screwfix) | 14-inch | 50mm | Chrome vanadium steel head, drop-forged cast iron handle. 5/5 Screwfix reviews. The 50mm opening fits 40mm waste fittings without stepping up to 18-inch. Best value for extension plumbing. |
| Irwin Record Stillson (Screwfix) | 14-inch | 38mm | Professional benchmark. BS 3594 compliant (drop-forged, dimensionally accurate). Flame-hardened V-shaped teeth, tighter jaw mechanism. Slightly smaller opening than Magnusson, so check your fitting sizes. |
At Toolstation, the Dickie Dyer 18-inch Heavy Duty (both steel and aluminium versions) offers good value if you need the larger size for waste connections or external pipework.
The UK has its own pipe wrench heritage. Footprint Tools of Sheffield has been manufacturing pipe wrenches since Thomas R. Ellin registered a pipe wrench design in 1889. They produced their 10 millionth pipe wrench in 1958. The company survived recession, was revived in 2009, and still manufactures in Sheffield under fourth-generation family ownership. Their compact 9-inch model is still available at Screwfix if you want a genuinely British-made tool.
What to buy for an extension project
For second-fix plumbing on a kitchen extension or bathroom renovation:
- One 14-inch pipe wrench (primary): £25-40
- One 10-inch or 12-inch pipe wrench (backup/tight access): £10-20
- Total: a pair for less than the cost of a single plumber callout
That pair, combined with a pair of adjustable wrenches for hex fittings and compression work, covers every wrench task across the project.
Pipe wrench vs adjustable wrench
These tools do different jobs. Using the wrong one creates problems.
A pipe wrench grips round surfaces. The serrated jaws dig in. It's for iron pipe, steel pipe, round fittings, and anything cylindrical that needs turning.
An adjustable wrench grips flat surfaces. The smooth, parallel jaws fit hexagonal nuts and bolt heads. It's for compression fittings, tap connectors, isolation valves, and any fitting with flat sides.
Use a pipe wrench on a chrome tap connector and you'll gouge the finish. Use an adjustable wrench on a round iron pipe and it'll slip off. Match the tool to the surface shape and you won't damage fittings or injure yourself.
Where you'll need this
- Second fix plumbing - gripping and tightening larger fittings such as waste traps, bath taps, and boiler connections
Pipe wrenches are used during the plumbing stages of any extension or renovation project. They appear whenever threaded iron or steel connections need making or breaking, and when waste fittings need serious grip to tighten or remove.
Common mistakes
Using it on chrome or plastic fittings. The serrated jaws score chrome permanently and crack plastic under stress. Use an adjustable wrench for hex fittings, hand-tighten plastic, and keep the pipe wrench for iron and steel only.
Starting with zero jaw gap. If the jaws clamp tight before you pull, the cam action can't engage. Leave the gap described in the technique section above. The wrench does the gripping; you just provide the turning force.
Using only one wrench. The pipe rotates with the fitting. The joint at the other end of the pipe run comes undone, or the pipe snaps at a corroded weak point. Use a backup wrench on the pipe while the working wrench turns the fitting.
Forcing it in the wrong direction. Pipe wrenches only grip one way. If you're pushing and the teeth are skating across the surface, you're going the wrong direction. Flip the wrench or reposition it.
Over-tightening threaded joints. Follow the tightening guidance in the warning above. Cranking harder strips the threads or cracks the fitting. PTFE tape on the threads does the sealing work, not brute force on the wrench.