Impact wrench torque guide

What the ft-lbs on the box means

The torque figure on an impact wrench is the most it can deliver in the loosening direction when the anvil hammers a seized fastener. It is a ceiling, reached for a fraction of a second at a time, and it says nothing about how tightly the tool will leave a nut when you run it in the other direction. The Bluebow 1/2 inch wrench is sold in three tiers, 737.5, 900 and 960 ft-lbs, and every one of them will break loose any lug nut on a car or a light truck; the higher tiers earn their keep on fasteners that have rusted in place on trailers, tractors and old iron.

Tightening is a different job. An impact wrench has no way of knowing when a nut has reached the figure your vehicle maker specified, and the figure matters: too loose and the wheel works on its studs, too tight and the studs stretch. That is why the tire trade's own procedure ends with a wrench that can be calibrated, not with the impact.

What lug nuts are tightened to

The chart below is a selection from the 1995 to 2021 lug nut torque chart compiled by James Halderman, an automotive textbook author, for cars, light trucks, SUVs and vans, with two rows for trailer wheels from the Load Trail wheel torque sheet. Your owner's manual is the figure that counts; the chart shows how narrow the range is.

The passenger rows are read from the 1995 to 2021 chart; the Load Trail sheet tightens in three stages and asks for a re-check at 50 miles.

Read the chart against the wrench: every passenger figure sits below 160 ft-lbs, while the lowest Bluebow tier breaks loose at 737.5. The gap is the point. The wrench is for taking a wheel off and for snugging it back on; the number in the manual belongs to a torque wrench.

The four steps the tire trade teaches

The Tire Industry Association teaches wheel installation as four letters, R.I.S.T., and Modern Tire Dealer spelled them out in an editorial we read: remove debris from the wheel's mating surfaces, inspect every component, snug the lug nuts in a star pattern starting at 12 o'clock and crossing the center of the wheel, never around in a circle, and torque to the value the vehicle manufacturer specifies with a wrench you can calibrate.

The impact wrench belongs to the S. Run the nuts on in the star pattern at low speed until they seat, and stop. A wheel left at impact torque is a wheel tightened to whatever the tool happened to deliver, which is not a number anyone wrote down.

Which Bluebow tier to pick

For a car, a crossover or a half-ton pickup, the 737.5 tier does everything the wheel asks and most of what the suspension asks. The 900 tier is for trucks, trailers and farm equipment, where bolts seize over a winter and the extra torque saves the breaker bar and the heat. The 960 tier is for shops and farms with old iron: implement pins, rims on a tractor, the frame bolt nobody has touched in a decade.

All three share the brushless motor, the three speeds, the brake stop that keeps a loosened nut on the stud, the LED, two 21 V 4.0 Ah batteries, four impact sockets in 17, 19, 21 and 22 mm and a case. We put four impact sockets in the case for that reason: a chrome hand socket from a ratchet set can crack under the hammering.

Eyes, hands and hours

A socket that slips off a rusted nut throws chips, and OSHA's eye and face protection rule asks for eye protection with side shields wherever particles fly, fitted over prescription glasses without moving them. An impact wrench is also a vibrating tool. NIOSH's bulletin on vibration syndrome names grinders, drills and high-speed rotating hand tools, describes the numbness and blanching of the fingers that follow years of exposure, and gives the work practices: grip the tool as lightly as safe control allows, rest it on the work, keep your hands warm and dry, and take a ten-minute break after each hour of continuous use.

The torque figures and the four steps on this page are the ones the Bluebow selection holds every impact wrench page to; the wrench itself is on the impact wrenches shelf.