Flex
Flex 24V FX3171A Variable Speed Angle Grinder
Flex's flagship 24V grinder, part of the brand's 2021 North American relaunch. A sensor-free brushless motor spins 4-1/2 or 5-inch wheels at up to 10,000 RPM - the highest top speed in this roundup - with touch-control speed settings of 3,500/5,000/7,000/10,000 RPM. Anti-kickback sensing stops the motor on bind-up, guard adjustment is one-step tool-free, and the vibration-suppression side handle tames buzz. FX3171A is the no-lock paddle version; FX3181A is the side-switch sibling. THERMA-TECH heat management and 24V packs push it toward corded-class sustained output.
Specifications
Features
Pros
- ✓10,000 RPM top speed leads the cordless 5-inch class - cut-off wheels feel noticeably faster than 8,500-9,000 RPM rivals.
- ✓Four real speed settings (3,500-10,000 RPM) via touch control make it a legitimate flap-disc, sanding, and polishing tool, which is rare on cordless grinders.
- ✓Kickback sensor stops the motor automatically if the wheel binds - PTR verified it works.
- ✓Light for the power class at 4.2 lbs bare, and owners call it well-balanced with low vibration from the suppression handle.
- ✓24V platform with THERMA-TECH heat management sustains output better than most 18V packs under long grinds.
- ✓One-step tool-free guard adjustment is faster than the detent systems on most competitors.
- ✓5-year warranty with registration, and Pro Tool Reviews concluded it 'competes very well against premium professional models'.
- ✓Kit with 5.0Ah battery and 160W fast charger frequently discounts to around $210.
Cons
- ✗No electric release brake - PTR measured about 2.5 seconds for a Type 27 wheel to spin down after letting go, behind Bosch/Makita brakes.
- ✗Flex 24V is a young platform in North America with a smaller tool catalog and fewer battery promos than DeWalt/Milwaukee.
- ✗$199 bare is premium pricing, and 24V batteries are expensive if you are not already invested.
- ✗Paddle has no lock-on, which fatigues hands on long grinding sessions (the FX3181A side-switch version fixes this).
- ✗Touch-control speed buttons can be fiddly with gloves compared to a mechanical dial.
- ✗Sold mainly through Lowe's and specialty dealers - fewer places to handle one in person or get quick warranty swaps.
- ✗No dust-extraction ecosystem integration like Makita AWS or Bosch's connected modules.
Compare the Flex 24V FX3171A Variable Speed Angle Grinder
Related tools
More from Flex →
Milwaukee's braking M18 Fuel grinder, rated equivalent to an 11-amp corded tool with an 8,500 RPM brushless motor. The paddle-switch no-lock configuration is the OSHA-friendly pick; slide-switch and variable-speed siblings (2888) fill out the family.
DeWalt's Power Detect flagship grinder: it senses larger batteries and raises output to 1,350 watts, spinning to a class-leading 9,000 RPM. The Kickback Brake and E-Clutch electronics shut the wheel down on pinch events before the tool wrenches your wrist.
Makita's long-running brushless LXT grinder with Automatic Speed Change: it drops RPM and raises torque under load to keep the wheel moving. The slide switch with lock-on suits continuous grinding; a paddle-switch sibling (XAG09) covers no-lock jobsites.