I'll never forget the first time I slipped while driving a slot-head wood screw using my Yankee push drill. The bit drilled a 1/4-inch hole right through my thumb. It was the mid-1970s, when I was still banging in finish nails by hand, and having sore–and injured–fingers was part of the job.

Impact drivers get their name from the pounding action of the hammer connected to the motor against the anvil attached to the bit holder.
Photo: by dotfordot.com Impact drivers get their name from the pounding action of the hammer connected to the motor against the anvil attached to the bit holder.

My fingers started to heal in the early 1980s, about the same time the first cordless drills came out. I thought I had died and gone to 9.6-volt heaven–but the best was yet to come when, some 20 years later, I got my first cordless impact driver. I haven't let go of that tool since.

If you don't know about impact drivers, let me tell you about one of the greatest tools that's ever been invented next to the nail gun, table saw, and power miter saw. Just like an auto mechanic's pneumatic impact wrench, the rotation of the impact driver delivers hammering force, adding a lot of torque without a lot of reaction force. Inside the tool, attached to the back of the bit holder is a two-lugged gear called the anvil. A drive gear with two matching lugs (the hammer) repeatedly strikes the lugs of the anvil when the torque needed to turn the bit exceeds the torque of the tool's rotational force alone. Similar to the blows per minute of a rotary hammer, impact drivers are measured in impacts per minute.

Put simply, an impact driver runs like a very fast drill until you need more torque to drive a screw. Then the hammer hits the anvil about 50 times per second and drives the screw with hundreds of little hits. Finish carpenters' 12-volt drill/drivers ramp up to about 250 inch-pounds of torque, while early impact drivers topped out at about 700 inch-pounds. But some new lithium-ion impact drivers approach 1,500 inch-pounds–a huge difference. You'll rarely strip the head of a screw with an impact driver, but you can shear one off easily.

The Tools

We set out to test the latest 18-volt lithium-ion impact drivers, but we made a few exceptions to round out the field. All but the Bosch are LI-powered, but a few different voltages and tool configurations are in the mix. The 14.4-volt tools include the Hilti SID144-A and Panasonic's EY7540LN2L and EY7542LN2L combination impact/clutch-controlled driver. The 18-volt tools are the Bosch 23618, DeWalt DC827KL, Hitachi WH18DL, Makita BTD141 and BTD142HW compact, Milwaukee 0881-22, Ridgid R8823, and Ryobi P230. The Craftsman 320.28128 is the only 20-volt tool.

Flexible Fuel. The Bosch is limited to nicad batteries, but many of the drivers also can be powered by their brand's nicad or NiMH batteries of the same voltage, including the DeWalt, Hitachi, Milwaukee, Ridgid, and Ryobi. The Ridgid can even use 24-volt LI batteries. Makita's compact model is smaller because it has a half-sized battery with reduced runtime but full 18-volt power. Hitachi just introduced a similar compact version, but it was too late for our test.

Similarities. Functionally, these tools are very similar. All have variable speed triggers, automatic brakes, through-handle direction switches with lockoff position, and headlights. Impact drivers have 1/4-inch hex bit holders that hang on to bits with a ball-bearing detent system for a vibration-proof grip and quick bit changes.

Combination Tool. Panasonic's EY7542LN2L is an impact driver with a separate, nonimpact driver mode controlled by clutch settings. This tool saves you from having to keep a separate drill on hand for drilling holes, as an impact driver is probably one of the worst tools to use with a drill bit. This tool also is safest for driving soft brass screws or steel screws against hardware

On-the-Job Performance

Waiting just long enough to charge the batteries, we took the tools into the field. My crew used them to set hollow-metal jambs, screw down underlayment, do light framing, you name it.

At first, all the carpenters balked at using 18-volt drivers. Few of the finish guys felt they needed a heavier or more powerful impact driver; they were more than satisfied with their 12- and 14.4-volt tools. But the results from the field were telling. The new LI tools outperformed their nicad and NiMH tools big time, with a definite weight advantage. Many of the new 18-volt impacts weigh no more than their older, 14.4-volt non-LI counterparts, making the trade up a no-brainer. The guys in the field gravitated to the lighter models even before we ran the head-to-head tests, so weight was a factor in choosing our favorites. But that wasn't all.

Ergonomics. The most significant difference between these tools is the way they feel in your hand, and that includes their weight, balance, overall size, and grip circumference.

A big part of the comfort level is being able to wrap your hand all the way around the grip. From carpenters with plate-sized hands to carpenters with smaller paws, we found the smaller the driver, the more enjoyable it was to use for everybody. The DeWalt, Hilti, Makita, and Panasonic tools were picked up the fastest. The big guns–Bosch, Craftsman, Milwaukee, Ridgid, and Ryobi–were the least popular on the jobsite.

Belt Hooks. Being on my jobs means climbing ladders, carrying materials, and crawling around cabinets. That's why belt hooks or clips were the next feature the crew wanted. But not every tool has them.

The best belt hooks are adjustable to help balance the tool on your belt, no matter whether you are kneeling or climbing a ladder, and all are reversible. The Panasonic's adjustable hooks are the best, and the Hitachi's hook is similar. But both of these crowd your grip when you hold each one in the left hand.

The pop-up Bosch belt clip is too short to engage securely in a toolbelt; I wouldn't trust it with anyone underneath me. The Makita 141 has a reversible belt clip, but not the 142, although the same clip fits on either tool. The DeWalt also fits an optional clip on either side, but it will not come with the tool until the summer. The rest of the tools don't have belt hooks or clips.

Lights. Every driver has an onboard LED light, which proved to be a big hit with the carpenters. With dark corners and cabinets everywhere on a jobsite, there's nothing more helpful that having good light, especially when you want to seat a screw just right. We found that lights bearing directly on the screw head were best. Two designs work well: a nose light like Hilti's, which has three LEDs encircling the bit holder, and trigger lights located just above the trigger, as found on DeWalt, Makita, Milwaukee, Ridgid, and Ryobi. Lights mounted on the battery housing or bottom of the handle were noticeably less focused and didn't provide enough illumination like those on the Bosch, Craftsman, and the Panasonics. (Panasonic has the brightest lights.) The Hitachi's light is on the tip of the belt hook, which provides aim-able light but only on one side.

Bright white lights are more effective than the amber-colored lights of the Bosch and Hitachi. Everyone appreciated how the Makita lights stay on for 12 seconds, then fade out. This lets you avoid an annoying strobe effect when feathering the trigger in a dark cabinet, and also lets you find a dropped screw without running the motor.

Some of the tools reserve the first part of the trigger pull for their lights, and this was handy for lining up the bit on a screw without spinning it. It also made for a useful impromptu flashlight. The tools with this feature are the Bosch, DeWalt, Hilti, and Makitas. The lights on the Hitachi and Panasonic tools are manually switched and stay on a few minutes after putting the tool down, and Bosch's light can be disabled.