Collection: Accessories

What are impact rated bits, and do you need them?

An impact driver does not drive a screw with steady rotation. It hammers, delivering thousands of short rotational blows per minute. Every one of those blows is a torque spike travelling up the bit, and that is a very different load from what a drill applies.

A standard driver bit is hardened all the way through to make the tip as hard as possible. Hard also means brittle. Put one in an impact driver and it does not wear out gradually — it snaps at the shank or shears the tip off, usually at the worst moment, sometimes leaving half a bit in the fastener.

An impact rated bit is heat-treated in zones instead. Milwaukee's SHOCKWAVE bits keep a hard, wear-resistant tip for fit and grip, and leave a section of the shank — what Milwaukee calls the SHOCKZONE — slightly softer so it can flex and absorb the spike rather than transmitting all of it to the tip. The bit gives a fraction of a degree, springs back, and survives.

So the answer to the common question is yes, if you own an impact driver. And the useful part is that it works the other way round too: impact rated bits are perfectly happy in a drill or a manual driver, so one set covers everything and you are never asking whether the bit in your hand is the right kind. The same rule applies to bit holders, extensions and adapters. A hardened accessory in the chain is the part that will break, so if the bit is impact rated, the holder should be too.

What bits go in an impact driver

Almost every cordless impact driver made in the last twenty years takes a 1/4 in. hex shank, held by a spring collet. That is an industry standard rather than a brand fitting, so bits and holders move freely between brands. The exceptions are drill bits and hole saws with round or threaded shanks, which need a chuck or an arbor.

Matching the bit to the fastener matters more than most people credit, because a poor fit is what rounds out screw heads. Phillips PH2 is still the most common tip in general construction. Square drive is standard on decking and cabinet screws in North America. Torx has taken over structural screws, self-drilling fasteners and most equipment work because the six-lobe geometry does not cam out under load. Hex bits handle set screws and machine hardware, and nut driver bits let an impact driver run small hex-head fasteners without changing to a socket.

A large mixed kit is worth having for that reason alone: it means you never talk yourself into using a PH2 on a Torx head because it is what is in the driver. Fresh tips also grip better than worn ones, so replace a bit when the corners look rounded rather than when it finally breaks.

Retention is the other half of the job. A magnetic bit holder keeps the screw on the tip so you can start a fastener one-handed overhead. Magnetic holders that mount to the tool itself — an adhesive-backed silicone pad, or a screw-on tray for the drill body — keep the next four or five bits where your hand already is, which is most of the time saved on a repetitive install.

Drill bits and cutting wheels by material

Matching the bit to the material is the whole game. Steel, masonry and sheet metal each want a different tip geometry, and using the wrong one burns the bit rather than cutting the hole.

Metal. High speed steel with a black oxide finish is the general-purpose answer for mild steel, and the oxide finish both resists corrosion and holds cutting fluid on the flutes. Run slower than you think, keep steady pressure so the bit cuts rather than rubs, and use fluid on anything thicker than sheet. Heat is what kills a drill bit in metal, not the work.

Concrete, brick and block. These need carbide, and the bits here are carbide hammer drill bits with a precision ground tip that starts without walking and wide flutes that clear dust quickly — dust in the hole is what causes bits to bind and heat up. Usefully, this kit uses a 1/4 in. hex shank, so it runs in an impact driver as well as a hammer drill, which means you can hang a few anchors without carrying a second tool.

Cutting metal. Thin bonded cut-off wheels for a 4-1/2 in. angle grinder handle rebar, heavy wall pipe and sheet. A thin kerf cuts faster and generates less heat than a thick one, which is why 0.045 in. has become the site standard. Two rules matter: check that the wheel's arbor size matches your grinder, and never run a wheel on a grinder whose speed exceeds the wheel's own maximum rating. Keep the guard on.

Milwaukee step drill bits and how the numbering works

A step drill bit is a cone of progressively larger cutting steps, and it exists for sheet material: panel boxes, enclosures, junction boxes, ducting, thin plate. One bit produces a whole range of hole sizes, it deburrs the hole as the next step passes through, and it will not grab and spin the workpiece the way a twist drill does when it breaks through thin steel.

Milwaukee identifies each bit by a number, and the number tells you the range rather than a single size. The ones we stock cover the sizes that come up most in electrical and mechanical work:

• #4 — 3/16 in. to 7/8 in. in small increments. The general-purpose bit for small holes and cable glands.
• #8 — 1/2 in. to 1 in. in 1/16 in. steps. Fine control across the mid range.
• #9 — two sizes only, 7/8 in. and 1-1/8 in. Built for the conduit knockouts you cut most often.
• #11 and #12 — both start at 7/8 in. and run up to 1-7/32 in. and 1-3/8 in. respectively, for the larger end of an enclosure job.

Two-piece sets pair a small-range bit with a large-range one, which is the efficient way to buy if you are starting from nothing. There are also design differences worth knowing. Dual-flute bits cut faster and resist jamming; a single cutting edge gives more control and a cleaner finish. And one step bit here carries a 1/4 in. hex shank rather than a round one, so it runs in an impact driver as well as a drill.

Whichever you use, go slow, keep pressure steady, and use cutting fluid on anything heavier than thin sheet. Step bits are cheaper to lubricate than to replace.

Impact sockets and drive sizes

Impact sockets are not chrome hand sockets in a darker finish. They are forged from a tougher, slightly less hard steel with thicker walls, so they deform rather than shatter under the hammering of an impact wrench. Chrome sockets can crack and throw fragments on impact tools, so never fit one to an impact wrench.

Drive size is the square hole in the back, and it should match the tool and the fastener. A 1/4 in. drive suits small fasteners and tight access. A 3/8 in. drive is the general-purpose size for most mechanical and equipment work. A 1/2 in. drive is for lug nuts, suspension, structural bolts and anything else where you want the torque.

Depth is the next choice. A deep socket clears a long stud or a protruding bolt end, so it is the one you want for wheel studs and threaded rod. A standard socket is shorter and stiffer, which matters when clearance above the fastener is limited. Many people carry both in the sizes they use most and only one depth for the rest.

Six-point sockets grip the flats of a fastener instead of the corners, which is why they are standard on impact tools — they resist rounding a tight or rusted nut far better than twelve-point. Choose SAE or metric by what you actually work on, and note that the SHOCKWAVE sets use stamped and ink-filled markings rather than printed ones, so you can still read the size after a year in the truck. Some of these sets come in a PACKOUT-compatible case, which is covered on our tool storage page.