DeWalt 1/4 in drive 6-point deep metric impact socket (4 mm)

Why I reached for a 4 mm deep impact socket

Tiny fasteners have a way of derailing otherwise straightforward work. On small appliances, automotive trim, control modules, and the occasional piece of shop equipment, I routinely come across miniature hex hardware that demands a precise, deep‑reach socket. That’s where this 4 mm deep impact socket has been earning its keep for me. It’s not an everyday size, but when you need it, you need it to fit right, hang on to the fastener, and withstand some real torque without twisting out or rounding the corners.

Build and design

This is a 1/4 in drive, 6‑point, deep metric socket made from heat‑treated CR‑440 steel with a black oxide finish. In hand, it feels like a proper impact socket—thicker walls than chrome, a little more weight than its tiny 4 mm opening might suggest, and a cleanly machined bore. The overall length is right around two inches, which gives you the reach you want for nuts on protruding studs and clamps without being so long that it wobbles under power.

Black oxide is the right choice for an impact socket. It doesn’t sparkle like chrome, but it resists chipping and offers reliable surface protection if you keep it oiled or at least dry. After several weeks of normal use and living in a steel drawer, I’ve had no rust forming, just the expected light scuffing from contact with fasteners and anvils.

Fit, engagement, and the 6‑point profile

At this size, small variations in machining make a big difference. The machining here is tidy and consistent. The 6‑point opening is true and square, with a snug fit on 4 mm heads that doesn’t require tapping in or levering off. DeWalt’s DirectTorque geometry is subtle—you don’t see it at a glance—but it shifts contact away from the corners and onto the flats. On tiny fasteners that are easy to round, that matters.

I tested it on a mix of small hex nuts and machine screws used in lighting housings and electrical enclosures. Engagement was positive and there was minimal rotational slop on the flats. The socket also handled slightly marred hardware well, where a loose, corner‑contacting socket would slip.

Impact and hand tool performance

Although it’s impact‑rated, I’ve used this with both a compact 1/4 in impact wrench (pin detent) and a fine‑tooth hand ratchet. On the impact, the retention hole and groove are properly cut; with a pin and O‑ring, the socket stayed put even when I pulled it past a tight bend to reach a fastener on a bracket inside a cabinet. On the ratchet, the drive recess feels crisp, without the slop that sometimes shows up in very small deep sockets.

The deep body provides about 1‑3/16 in of bolt clearance past the nut engagement, which lets you run down long studs without bottoming out. Nut engagement depth is about 9/32 in—plenty for a small hex to be fully captured. That combination helped in a task that would give a shallow socket trouble: removing a pair of tiny hex nuts buried on protruding stand‑offs behind a plastic fascia. The socket swallowed the protrusion and still fully gripped the nut.

Real‑world use cases

• Small appliance and equipment panels: Many use small hex hardware that sits in recesses or behind trim; the deep length reaches cleanly without scraping.
• Automotive interior clips and micro‑brackets: Occasionally you’ll find 4 mm hex hardware on accessory mounts or aftermarket components. The deep body helps around protrusions and tight plastics.
• Electrical enclosures and lighting fixtures: Terminal covers and strain reliefs sometimes use small hex nuts; secure engagement is critical to avoid rounding.
• RC, hobby, and instrumentation: If you work with small metal frames or standoffs, the small size and deep reach can be indispensable.

Is 4 mm common? No—and that’s exactly why it pays to have an impact‑rated version on hand. When a tiny fastener fights you, you don’t want to be debating whether your chrome socket is going to split or round a corner.

Durability and finish

The heat‑treated CR‑440 steel holds up as expected from a branded impact socket. After repeated use on small hardware, I don’t see bell‑mouthing at the opening, and the internal corners remain sharp. The black oxide has scuffed, but that’s normal and purely cosmetic. Keep in mind that black oxide isn’t rust‑proof; a light wipe with an oily rag goes a long way.

One note on laser‑etched size markings: they are large and easy to read—remarkably so for a socket this small. In a drawer full of black sockets, that visibility saves time. Laser etching can fade with heavy abrasion over years, but after a few weeks of dirty, gloved use, the markings are still bright and intact.

Precision and control on tiny hardware

Small fasteners demand control as much as strength. The 6‑point profile and DirectTorque geometry gave me consistent, predictable bite without chewing up corners. That meant I could confidently break free snug hardware with an impact wrench set to low or use a hand ratchet to ease things off without slippage. Because it’s a deep socket with thicker impact walls, you also get a little more torsional stiffness than a flimsy thin‑wall chrome. That helps keep the axis straight when your access isn’t perfect.

Compatibility and retention

• Drive: 1/4 in square. Works with compact impact wrenches, battery ratchets, torque wrenches, and standard hand ratchets.
• Retention: O‑ring and pin compatible; stays locked on pin‑detent anvils and plays well with friction ring setups too.
• Outside diameters: The drive end is beefy enough for durability, and the nut end is slim enough to sneak into confined spaces for a deep socket. I had no interference issues on narrow channels inside housings.

Limitations and things to know

• It’s a specialty size. If you rarely encounter 4 mm hex hardware, this will sit more than it spins. For those who work on electronics, appliances, or instrumentation, it’s far more likely to pay for itself.
• No knurling. On a socket this small, knurling can be nice for finger‑spinning, but impact sockets rarely include it. Not a deal‑breaker, just something to note.
• Black oxide needs care. If you toss it in a damp toolbox, it can spot. A quick wipe after use is enough to keep it looking good.

Value and alternatives

Many mechanics default to chrome in small sizes, but this impact‑rated deep option fills a different niche: hard use in tight spaces with little tolerance for slip. It’s not a substitute for a complete set, but as a single, well‑made piece, it covers those occasional jobs where you’d otherwise be improvising with a nut driver or risking a rounded head. The machining quality, clear size marking, and secure retention make it feel like a professional piece rather than a filler socket.

The bottom line

After living with this 4 mm deep impact socket in my kit, I trust it for those fiddly hex fasteners that can bring a project to a halt. The combination of a true 6‑point bore, DirectTorque contact on the flats, deep reach, and proper retention on impact tools adds up to a small but genuinely useful solution. It’s built to be used hard and put away without worry, and it’s easy to grab when you need it thanks to the high‑visibility marking.

Recommendation: I recommend this socket to anyone who regularly encounters tiny metric hardware—appliance techs, automotive interior and accessory installers, instrument and electrical trades, and hobbyists who want a robust option for deep‑seated fasteners. It’s a specialty piece, but it’s well executed, confidence‑inspiring on delicate work, and tough enough for impact use when a stubborn fastener calls for it. If 4 mm is part of your world, this is a smart, reliable addition to your 1/4 in drive lineup.