A Stillson wrench grips and turns threaded pipe and fittings; its serrated, self-tightening jaws bite round surfaces without rounding them.
The trick is in the moving hook jaw and knurled adjusting nut. As you pull the handle, the pivoting jaw tilts and the hardened teeth rake forward, multiplying grip on a round surface. That bite is why a Stillson stays planted where smooth-jaw wrenches skate. See the dictionary entry for the term to see this bite-on-pull action described.
Credit for the design goes to Daniel C. Stillson, who secured a U.S. patent for an improved pipe wrench in 1869. His layout—fixed lower jaw, floating upper jaw, and coarse teeth—set the pattern that most pipe wrenches still follow today.
What a Stillson wrench does
A Stillson-pattern pipe wrench uses angled, serrated teeth to dig slightly into the work when you pull. Round pipe is tough to grab with flats; the Stillson solves that by combining a long lever, a springy joint between jaws, and teeth that rake. Opened to the right size, the hook jaw rides the crown of the pipe while the heel jaw backs it up. When you load the handle, the hook jaw cams forward and the bite increases, turning stubborn threads with control.
Most jobs involve threading, tightening, or breaking loose pipe nipples, couplings, elbows, tees, and unions. NPT threads tighten by interference, so the last quarter-turn can feel brutal; a Stillson supplies that last surge without rounding anything. Used in pairs, one wrench holds the fitting while the other turns the mating part, so the stress stays where you want it.
Stillson options, capacity, and best uses
| Type | Typical Pipe Capacity | Best Use |
|---|---|---|
| Straight Stillson | 1⁄4–6 in pipe | General runs, bench work, most fittings |
| Offset Stillson | 1⁄2–2½ in pipe | Tight clearances, over-obstructions, near walls |
| End (Short-head) Stillson | 1⁄2–1½ in pipe | Close quarters, limited swing around valves |
| Aluminum-body Stillson | Match steel sizes | Overhead work, long carries, service calls |
Inside the cam action
Look closely at the hook jaw and you’ll see the teeth lean forward. That lean, plus the floating jaw, creates a cam. When you pull, the jaw pivots a few degrees and those teeth dig just enough to lock. Release the pull and the jaw relaxes so you can reposition without thread damage.
Jaw geometry and teeth care
Pipe wrench teeth are case-hardened so edges stay crisp while the body stays tough. The heel jaw carries broad flats that steady the bite; the hook jaw does the cutting. If teeth pack with lead tape or dope, scrub them out so the bite returns. Avoid grinding the teeth; swap jaws instead so the geometry stays true.
Straight, offset, or end style
Straight styles line up with the pipe and give you the longest lever for the weight. Offset heads swing past framing, tanks, and sheet goods that block a straight shot. End styles carry a compact head and pull in tight circles where swing is limited. Many techs own a straight pair and add one offset for tight plant rooms.
Common grip mistakes and easy tweaks
- Jaw too loose: Tighten the knurl until the hook kisses the pipe, then test with a short pull.
- Jaw too tight: Back off slightly so the head can tilt and cam instead of skating.
- Wrong jaw orientation: Flip the wrench so the hook points toward the pull.
- Biting near an edge: Move off the fitting edge; let both jaws seat fully on round stock.
- Cheater pipe: Size up the wrench instead to keep control and protect cast parts.
Taking a Stillson wrench into real jobs
Plumbing and gas lines
On water or gas piping, place the hook jaw on the side you’ll pull toward. That way the jaw climbs the pipe as you pull, not away from it. Seat as much tooth as you can without bottoming the jaw on the pipe. For unions and couplings, park a second wrench on the opposite part so the torque doesn’t twist the run.
On gas work, make up joints with steady force and check alignment as you go. On water lines, snug, back off, then snug again to spread compound evenly. If a nipple collapses, move to the next size up with more engagement on the crown.
Heat cycles can freeze a union. Back the nut a touch, then tap the joint body with a dead-blow mallet and try again with a steady pull. If space allows, match wrench sizes so both hands feel the same pull.
On vehicles, the wrench helps where a muffler clamp has fused or a thin tube has no flats left. Protect neighbors—hoses, wires, sensors—when the wrench breaks the part loose. Keep pulls smooth so you don’t kink a tube.
Copper and soft metals mark fast. Either pad the bite or grab a strap wrench. If you must bite, plan for cosmetic cleanup later.
Hydronic and steam work
Old radiators and boiler loops often hide thread compound that has set like glue. Load the wrench with a smooth, steady pull, not a jerk. If the joint stares you down, increase handle length by stepping up a size instead of sliding on a cheater bar that could crack the casting or launch the wrench.
Auto and field repairs
A Stillson can rescue round or thin-walled parts the moment a six-point socket stops gaining ground. Think seized exhaust sleeves, press-fit tubes, or farm fittings that no longer have flats. Protect soft tubing with a short wrap of scrap leather or an old belt before you engage the teeth.
When not to use one
Skip plated faucets, valve stems, and delicate chrome. Use a strap wrench for those. Skip hex nuts and bolt heads; that’s the world of sockets and spanners. And don’t smack the handle with a hammer or add a cheater pipe—both moves invite slips, bent jaws, and injuries.
Stillson, strap, and chain wrenches
A strap wrench wraps a wide belt around polished stock and grips by friction. It leaves no tooth marks and shines on finished fixtures and glossy pipe. A chain wrench loops a toothed chain and locks like a bicycle chain around a sprocket; it grips odd shapes and big diameters.
Stillsons move threaded work fastest. Straps protect surfaces. Chains tame large or irregular parts. Most pros carry at least one of each so the right grip is always on hand.
Stillson wrench vs monkey wrench
Both are adjustable, yet they solve different problems. A monkey wrench has smooth, parallel jaws and loves flats—nuts, bolt heads, and squared valves. A Stillson has offset, serrated jaws that grab rounds—pipe and fittings. Use each where it belongs and you’ll move faster and mark up less.
A quick test: if the work has flats, reach for smooth jaws; if it’s round, reach for teeth. If you only own a Stillson, you can still turn a square plug by biting the corners—just know you’ll leave marks. If finish matters, swap to a smooth-jaw tool.
Using a Stillson wrench the right way
Set jaw size
Spin the knurled nut until the hook jaw just slides over the pipe with light contact at two or three teeth. If the jaw has to detour far to one side to catch, go up a wrench size. Too loose and you’ll bruise the pipe; too tight and the wrench won’t cam.
Pick the pull direction
Point the hook jaw toward the direction of rotation. On a right-hand thread you’ll usually pull counterclockwise when viewed from the end of the pipe; on a left-hand thread the pull flips. Keep your free hand off the head so it can tilt and bite.
Use two wrenches when needed
Place a second wrench to hold the stationary part. Think of one wrench as the driver and the other as the brake. That split keeps stress off anchors, hangers, and the rest of the run.
Protect finished surfaces
Wrap polished or plated parts with leather, a rubber strap, or a layer of tape before you bite. Better yet, swap to a strap or chain wrench for those parts so teeth never touch.
Mind safety
Stand so a slip won’t carry your knuckles into anything sharp. Pull with your palm up when you can; it keeps fingers clear if the tool breaks loose. Retire any wrench with sprung jaws or chipped teeth. See the OSHA hand-tool rule about removing sprung or unsafe wrenches.
Work with your body
Keep shoulders square to the pull. Pull in a straight line with the pipe centerline, not off at a big angle. If the wrench pops, your weight won’t carry you into a beam or sharp edge.
Reset between pulls
Once the joint moves, back off the jaw a hair, roll it forward, and re-seat. Short, controlled bites beat wild swings in tight spaces.
Temperature and sealants
Cold joints feel stubborn. A small dose of heat on the fitting body—not the pipe thread—can help. When reassembling, pick a thread sealant that suits the fluid and temperature range for the system you’re building.
Task-to-wrench picker
| Job | Recommended Wrench Size | Notes |
|---|---|---|
| Tighten a 3⁄4-in coupling | 12-in straight | Good reach with solid bite |
| Break loose a 1-in union | 14- or 18-in straight | Add a second wrench to hold |
| Work near a wall on 1-1⁄4-in pipe | 18-in offset | Jaw angle clears obstructions |
| Spin short nipples out of a tee | 10-in end-style | Short head fits tight quarters |
| Overhead run, 2-in pipe | 24-in aluminum | Length without the weight |
Care, maintenance, and lifespan
After a messy job, back the jaw off and rinse out thread paste, grit, and metal chips. Brush the teeth clean so the rake stays sharp. A light oil on the adjusting nut and pivot points keeps the action smooth. If teeth round over or the hook jaw rocks side-to-side, install replacement jaws instead of tossing the whole tool.
Check the frame for cracks near the jaw housing and along the I-beam. Sight down the handle; twist or bend calls for replacement. Store it with the jaw relaxed.
Jaw sets and springs are wear parts. Keep a spare set in the truck so downtime doesn’t cost you a call. When you replace jaws, torque fasteners to spec and check engagement on scrap before heading back to the line.
Many makers stamp capacity on the handle; treat that as a hard limit. If you keep bumping against the limit, add the next size to your kit.
Choosing size and build
Wrench length sets torque. A 10- or 12-inch covers sinks and small appliances; 14- and 18-inch sizes handle most house runs; 24- and 36-inch tools live in commercial work. Pick the smallest wrench that holds without slipping—you’ll feel steadier and mark less metal.
So what is a Stillson wrench used for? Turning threaded pipe and fittings with strong, controlled bite—on water lines, gas piping, boilers, and shop rigs. Set the jaw, point the hook the right way, and pull smooth. Use two when you need to keep a run from twisting. Treat the teeth and pivots well and the tool will pay you back for years.
Once you learn the feel, a Stillson becomes second nature. It rewards steady hands, clean teeth, and the right match of size to task. That’s why the same jaw pattern Stillson drew up still earns its place on modern jobs.