Hacksaws: Blade Selection, Proper Technique, and What to Buy

Your plumber has gone home for the day and you need to shorten a piece of threaded rod for a bracket. You grab the hacksaw from the toolbox, push through the rod, and the blade wanders sideways, leaving a jagged cut at an angle. The nut won't thread onto the damaged end. You file it, try again, file some more. Twenty minutes on a job that should take two. The blade was loose, the wrong TPI for threaded steel, and installed backwards. A hacksaw is one of the cheapest tools you'll buy for a build. It's also one of the easiest to use badly.

What it is and when you need one

A hacksaw is a hand-powered saw with a thin, fine-toothed blade held under tension in a metal frame. It's designed to cut metal: copper pipe, steel threaded rod, angle brackets, conduit, and fixings. It also cuts plastic pipe and conduit, though with caveats covered below.

Two sizes exist. A full-size hacksaw takes a 300mm (12-inch) blade and handles most cutting jobs on a build. A junior hacksaw takes a 150mm (6-inch) blade and fits into tight spots where the full-size frame can't reach, such as cutting a pipe against a wall or trimming conduit inside a joist bay. Most homeowners need both. Combined, they cost under ~£15.

You won't use a hacksaw every day on a build, but when you need one, nothing else does the job as easily. Shortening a length of threaded rod to hang a bracket. Cutting copper pipe where a pipe cutter won't fit because the pipe runs too close to a wall. Trimming a metal bracket to length. Cutting plastic waste pipe or electrical conduit on site. These are quick, one-off cuts that don't justify setting up a power tool.

Full-size vs junior

These aren't just different sizes of the same tool. They serve different purposes.

The full-size hacksaw is your primary cutting tool. The junior is a companion for access problems. Don't try to cut a 22mm copper pipe with a junior hacksaw if you have room for the full-size. The shorter blade, softer steel, and lack of adjustable tension mean slower cuts and less control on anything substantial.

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Blade types and TPI

TPI stands for teeth per inch. It's the single most important specification on a hacksaw blade, and getting it wrong is the most common beginner mistake. The rule is simple: more teeth for thinner material, fewer teeth for thicker.

The underlying principle: at least three teeth must be in contact with the material at any point during the cut. If only one or two teeth engage, they catch and strip. On thin-walled copper pipe, a coarse 18 TPI blade has teeth so widely spaced that only one or two contact the pipe wall at a time. The blade judders, damages the pipe, and produces a rough cut. On thick steel rod, a 32 TPI blade clogs because the tiny teeth can't clear chips fast enough.

Bi-metal vs carbon steel vs all-hard

Blade construction matters almost as much as TPI.

Bi-metal blades bond a high-speed steel (HSS) cutting edge to a flexible spring-steel body. The HSS teeth stay sharp while the spring steel absorbs vibration without snapping. These are the right choice for DIY. They're forgiving of imperfect technique, unlikely to shatter, and last through dozens of cuts.

Carbon steel blades are the cheapest option, around £1 – £1 per blade in budget 5-packs from Screwfix or Toolstation. They work for light-duty cuts in copper and plastic but dull fast on steel. Fine for occasional use. Expect to replace them after a few jobs.

All-hard (HSS) blades cut straighter and faster than bi-metal because the entire blade is rigid. But they're brittle. Any flex, twist, or lateral force snaps them. Experienced metalworkers prefer them for bench work where the cut is controlled and the workpiece is firmly clamped. For site work where you're cutting at odd angles in tight spaces, they break too easily. Stick with bi-metal until your technique is solid.

How to use it properly

Most people pick up a hacksaw and start sawing. That works, sort of. But the difference between a clean, straight cut and a ragged, angled mess comes down to five things: blade direction, tension, starting technique, stroke length, and pressure.

Blade direction

Teeth point away from the handle. The hacksaw cuts on the push stroke. This is non-negotiable for normal use. If you install the blade backwards (teeth toward the handle), the saw pushes the material instead of cutting it, and the blade buckles.

Blade tension

This is where most beginners go wrong. A loose blade wanders sideways, bends under cutting pressure, and produces curved, angled cuts. The blade must be tight.

Tighten the wing nut until the slack is gone, then give it three more full turns. The blade should produce a slight "ping" when you pluck it like a guitar string, not a dull thud. You won't measure the tension precisely, but the ping test and the three-turns rule have worked for decades.

On some budget frames, the tensioning screw thread is too short to achieve proper tension. If you can't get the blade tight enough, add a washer or two between the nut and the frame to extend the effective thread length. It's a common modification.

Starting the cut

Don't just press the blade against the workpiece and start pushing. The teeth will skip across the surface, scoring the material and never biting in.

Use your thumb to guide the blade for the first two or three strokes. Place your thumb on the workpiece just beside the intended cut line, rest the blade against your thumbnail, and draw the blade backward (toward you) gently to create a small groove. Once the groove is established, remove your thumb and switch to forward push strokes. On harder materials like steel, nick the starting point with a flat file first to give the teeth a V-groove to bite into.

Stroke technique

Use at least 75-85% of the blade length on each stroke. Short, jabby strokes wear out the middle section of the blade while the outer teeth stay sharp. Long, smooth strokes distribute the wear evenly and cut faster.

Apply moderate downward pressure on the push (forward) stroke. Almost zero pressure on the return (backward) stroke. Pressing down on the return drags the teeth backward across the material, dulling them without cutting anything.

Cutting speed

Roughly 40-60 strokes per minute. That's about one second per stroke. Rushing to 80-100 strokes per minute generates heat, dulls teeth, and reduces control. On harder materials like stainless steel, slow down further and consider applying a drop of 3-in-1 oil or rubbing a candle along the blade to reduce friction.

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Cutting specific materials

Copper pipe

Use a 24 TPI blade. Secure the pipe in a vice or pipe clamp. If you don't have a vice, brace the pipe against a solid surface with your free hand well clear of the blade path.

After cutting, the inside edge of the pipe will have a burr, a small ridge of copper rolled inward by the blade. This matters. On soldered joints, the burr restricts water flow and creates a ledge where flux residue and debris collect. On push-fit joints, the burr can score or displace the rubber O-ring inside the fitting, causing a slow leak that won't show up until the system is pressurised.

Remove the burr with a round file (rat-tail file) or the deburring tool built into most pipe cutters. Two or three rotations inside the pipe end cleans it up. Also chamfer the outside edge slightly with a flat file so it slides into fittings smoothly.

Threaded rod

Use a 24 TPI blade. Threaded rod is awkward because the blade wants to follow the thread grooves rather than cutting straight across.

The nut trick solves this. Thread two nuts onto the rod past your cut mark. Tighten them against each other so they lock in place. Saw against the shoulder of the upper nut, which acts as a blade guide, keeping the cut square. After cutting, file a slight bevel onto the cut end, then spin both nuts off by hand. As each nut crosses the cut end, its threads re-form any minor damage from the saw.

Electrical conduit

Use a 32 TPI blade. Conduit is thin-walled, and a coarser blade will deform the tube rather than cutting it cleanly. Wrap a strip of masking tape around the conduit at the cut line. It acts as both a visual guide and prevents the blade from skating sideways on the slippery surface.

Checking your hacksaw is working properly

Hacksaws are simple tools, but a couple of checks prevent problems.

Blade condition. Hold the blade up to the light and look at the teeth. If teeth are missing, bent sideways, or the cutting edge looks shiny and rounded rather than sharp, the blade is done. Replace it. Forcing a dull blade through a cut requires more pressure, which causes the blade to wander and produces a rough finish.

Frame alignment. With a blade fitted and tensioned, sight along the blade from the handle end. The blade should be perfectly straight, not twisted or bowed. If the frame is bent (from being dropped or stood on), the blade will track at an angle. Budget frames bend easily. Mid-range frames with tubular steel construction resist bending much better.

Pin fit. The blade has a small hole at each end that sits on pins in the frame. If the pins are worn or the holes are elongated, the blade won't seat squarely and will twist during cutting. Check the pins when you change blades.

What to buy

Budget: £3 – £12

The Forge Steel 12-inch at Screwfix costs £3. It's basic: a stamped steel frame, minimal tension adjustment, plastic handle, and a 24 TPI blade that's adequate for a handful of cuts. For a homeowner who needs to make five or six cuts across an entire build, it does the job.

A better budget buy is the Minotaur 12-inch at Toolstation (£6.99, 150 five-star reviews). Sturdier frame, better handle, and the same 24 TPI blade. The Magnusson 12-inch at Screwfix (£11.99) adds a more comfortable grip and marginally better build quality.

For a junior hacksaw, the Eclipse 6-inch at Toolstation costs £3.48. It's the budget standard. The Roughneck at Screwfix (£8.29) adds a pistol grip that's easier on your wrist for longer cuts.

Mid-range: £15 – £30

This is where you get tools that last years, not months.

The Eclipse 70-20TR (around £15on Amazon, £16at specialist retailers) is Made in England by the Spear & Jackson Group, a company with over 260 years of manufacturing history. It has a die-cast alloy handle, tubular steel frame, and comes with an Eclipse Plus30 bi-metal blade. Community reviews cite 15-30 year lifespans. It's the tradesperson's quiet favourite.

The Bahco 317 (around £23at Toolstation, £17at Screwfix) comes fitted with a Sandflex bi-metal blade and a solid steel frame. It won the Auto Express hacksaw group test for build quality versus price. A reliable buy that'll last years.

The Irwin I-125 High-Tension (around £23) delivers 125 kg of blade tension and includes blade storage in the frame. It cuts well, but multiple forum users report the soft-grip handle deteriorating into a sticky mess after a few years. If long-term ownership matters to you, pick the Eclipse or Bahco instead.

The Bahco 325 Ergo (£22 – £28 on Amazon) adds ergonomic improvements and a 55-degree flush-cut position for cutting close to surfaces. It's the premium pick in this range.

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Alternatives

A pipe cutter (rotary wheel type) produces cleaner, squarer cuts on copper pipe than a hacksaw, with no burrs. If the pipe has enough clearance around it to rotate the cutter (about 50mm of space), it's the better tool for plumbing work. Pipe cutters for 15-22mm copper cost £5 – £15. But they can't cut threaded rod, brackets, conduit, or anything that isn't a round pipe. The hacksaw covers everything; the pipe cutter does one job better.

A reciprocating saw (powered) cuts metal, timber, plastic, and almost anything else with the right blade fitted. If you already own one for demolition or rough carpentry, it'll cut pipe and rod faster than a hacksaw. But it's overkill for the small, precise cuts a hacksaw handles, and it costs £60 – £150. Don't buy a reciprocating saw just to replace a hacksaw.

For cutting plastic pipe specifically, a ratchet pipe cutter (the type with a crescent blade that ratchets through the pipe wall) is the best tool. Clean cut, no burrs, no deburring required. They cost £8 – £15 and work on pipe up to 42mm diameter. Every plumber carries one.

Where you'll need this

• First fix plumbing - cutting copper and plastic pipe to length for supply and waste runs
• Drainage - cutting drainage pipe and fittings to size

A hacksaw appears wherever metal or plastic needs cutting to length on site. Shortening fixings, trimming brackets, cutting conduit runs. It's one of those tools that sits in the toolbox for days, then gets used three times in an afternoon.

Safety

Hacksaws are low-risk compared to power tools. The main hazards are minor but worth knowing.

Secure the workpiece before cutting. A pipe that rolls under blade pressure puts your hand in the path of the blade. Use a vice, pipe clamp, or at minimum brace the material firmly against a solid surface. Cutting freehand while holding the workpiece with your other hand works for quick jobs, but keep your fingers well behind the blade.

Wear safety glasses. Hacksaw blades can snap under tension, particularly all-hard blades and cheap carbon steel blades. A broken blade end can flick upward toward your face. Bi-metal blades are much less prone to this, but the habit of wearing glasses for any cutting work is worth building.