Bosch Self-Feed Bit Extension

Why I reached for this 6-inch bit extension

Rough-in week always reveals the weak links in a drilling setup. I picked up this 6-inch bit extension to get a little more reach for self-feed work through doubled plates and deep joists without stacking multiple adapters. After several days of boring holes for plumbing and low-voltage runs, I came away with a clear picture of where this extension shines and where it asks for a compromise.

Build and design

The extension feels like a purpose-built jobsite piece: tempered, hardened tool steel with a simple, no-frills finish. At about half a pound, it’s substantial without being clunky. The 7/16-inch hex shank and 7/16-inch receiver are the right fit for heavy self-feed work, especially with right-angle drills that prefer a hex shank for positive torque transfer.

The head is nicely machined. The bit seats fully and square, and the fit is snug enough that you don’t fight slop while lining up on the work. Runout at the tip of a mounted self-feed bit was minimal—exactly what you want when you’re starting a large diameter hole on a stud or plate and need the pilot screw to bite cleanly.

Bosch uses a set-screw/hex key retention rather than a quick-release collar. It’s old-school, but it’s also dead-simple and robust. The set screw bites into the flat of the 7/16 hex and holds with authority. There’s nothing spring-loaded to clog with dust or freeze up, and no collar to pull back with gloved hands.

Setup and compatibility

• Shank: 7/16-inch hex. Fits 1/2-inch chucks and any drill that takes a 7/16 hex.
• Receiver: 7/16-inch hex. Works with common self-feed bits in the 1- to 4-inch range that use a 7/16 shank.
• Length: 6 inches. Enough to clear doubled plates and reach around obstructions without excessive leverage.

If your kit is built around high-torque right-angle drills and hex-shank self-feed bits, this slots right in. If you run a traditional 1/2-inch chuck drill, the hex shank locks up fine in a three-jaw chuck. I used it with a Hole Hawg-style drill and a compact right-angle; in both cases the shank stayed secure and didn’t slip under load.

In use

I put the extension through typical residential tasks: dozens of 1-1/8 to 2-9/16-inch holes through SPF studs and plates, a handful through pressure-treated sill, and a few passes through engineered lumber. The extension didn’t flinch.

• Torque transfer: Solid. No sense of the shank twisting or the receiver rounding under heavy feed. When a bit stalled on a knot, the drill clutch or my wrist gave up before the extension did.
• Concentricity: Good. Wobble was negligible; holes tracked straight and the pilot screws pulled without chatter. You still need to let the bit feed itself—leaning on a self-feed bit is a good way to invite a bind—but the extension didn’t add any drama.
• Retention: The set screw stayed put. I snugged the bit once before starting and checked it a couple of times during the day. No loosening, no movement, and no witness marks beyond the expected small dimple where the screw contacts the flat.
• Chip clearance: A 6-inch extension will make chip evacuation more important. With large self-feed bits, back the bit out a couple of times on deep holes to keep chips moving. The extension itself doesn’t hinder that routine.

One small note: the extension’s plain steel finish is honest but not particularly grippy. A knurled section would make one-handed changes easier when your gloves are slick. It’s not a deal-breaker, just something I noticed when swapping bits on a ladder.

Durability and serviceability

The hardened tool steel takes the abuse well. After a rough few days—including some accidental drops—the hex corners on both the shank and receiver still looked crisp. No deformation of the set-screw seat, no burred edges, and the screw threads are still smooth.

I appreciate that a replacement kit (SF5018) is available. On extensions like this, the small parts are the wear points: set screw, perhaps the key, and depending on the kit, any retention hardware. Being able to refresh those pieces without replacing the whole extension is a practical nod to long-term use.

As with any bare steel accessory, wipe it down at the end of the day. A quick hit with a rag and a little light oil goes a long way against surface rust, especially if you work in damp crawlspaces or keep the kit in an unheated trailer.

The convenience trade-off

Let’s talk about the hex key. The set-screw retention is secure and simple, but it’s not fast. If you bounce among bit sizes constantly—1-3/8 for one run, 2-1/8 for the next, 3-inch for a vent—it’s an extra step every time. On days when I set up with one or two sizes and stayed on task, I barely thought about it. On days with frequent size changes, I missed a quick-change collar.

My workaround is basic: keep the key on a short lanyard clipped to the drill handle or tape a spare inside the lid of the bit case. That small habit turns the set-screw system from “annoying” into “fine.”

Safety and feel

A 6-inch extension introduces more leverage and a longer moment arm. That’s true of any extension, not just this one. Keep your stance square and the drill level, and let the bit’s lead screw do the work. I found the extra length helpful for clearing obstructions—pipes, Romex, insulation—without contorting into bad positions.

Kickback control on a high-torque drill is still on you, but the extension doesn’t exacerbate it. Alignment is predictable, and because the fit is tight, there’s no rattle that can translate into sudden grabs.

Value

This is a straightforward, pro-oriented extension without bells and whistles. The hardened steel, precise fit, and 7/16 hex on both ends are exactly what many tradespeople need. The price typically undercuts quick-release models, and you’re trading some convenience for durability and simplicity. If your workflow involves occasional bit swaps and a lot of repetitive drilling, the math favors this piece. If you’re on a crew that swaps diameters constantly, a keyless extension may earn back its premium in saved time.

What I’d change

• Add a knurled or lightly textured midsection for better grip during changes.
• Offer a captive set-screw design or a spare screw/key bundled in the tube.
• A light protective coating would help resist surface rust without adding cost.

None of these are essential; they’d just elevate the day-to-day experience.

Who it’s for

• Electricians and plumbers who primarily run one or two bit sizes all day.
• Remodelers who need occasional extra reach without rebuilding the whole drilling setup.
• Anyone using 7/16-inch hex self-feed bits and high-torque right-angle drills.

If your priority is the fastest possible bit change, look toward a quick-release extension. If your priority is a strong, tight, no-nonsense connection that you can trust to take torque, this fits the bill.

Recommendation

I recommend this 6-inch bit extension for pros and serious DIYers who value a secure, precise connection and don’t mind using a hex key to lock in their self-feed bits. It’s durable, the machined fit inspires confidence, and the 7/16-inch hex on both ends handles real torque without drama. The convenience compromise is real—quick-change extensions are faster—but the price, simplicity, and reliability make this a smart addition to a kit where most holes are drilled with one or two sizes rather than five. Keep the key handy, and this extension will quietly do its job for a long time.