The Milwaukee 3671-20 M18 FUEL 4-1/2"-6" Braking Grinder Slide Switch is a cordless angle grinder built for demanding cutting and grinding work on the M18 platform. This is a grinder designed for metal cutting, grinding, and general jobsite material removal. Model Number: 3671-20. If you want cordless convenience without stepping down in usable power, this is the one Milwaukee built to act more like a serious corded grinder than a light-duty cordless option.

On the job, the big story is output and wheel speed. Milwaukee rates it at 9,000 RPM and positions it as delivering 13 amp corded power, which matters because grinders either maintain speed under load or they bog down and waste your time. That kind of sustained performance makes a difference when you are cutting rebar, cleaning up welds, beveling edges, or knocking down stock in fabrication and repair work. Milwaukee also states up to 135 cuts per charge in 1/2 inch rebar when paired as shown with an XC8.0 battery, which gives you a clearer picture of what this tool is meant to handle.

The Milwaukee 3671-20 M18 FUEL 4-1/2"-6" Braking Grinder Slide Switch uses a POWERSTATE brushless motor and REDLINK PLUS electronics. In plain terms, that means the motor is built for hard use and the internal electronics are there to manage power, help protect the tool from overload, and keep performance consistent across the M18 battery system. That is the stuff you feel when a grinder stays productive during repeated heavy cuts instead of getting hot and soft.

Milwaukee also paid attention to control and day-to-day usability. The slide switch is designed for increased control, and the streamlined barrel grip helps the tool feel more manageable during longer work sessions. The included anti-vibration side handle matters more than it sounds like on paper, especially when you are grinding for a while and trying to keep the tool steady. There is also a spindle lock plus tool-free accessory and guard changes, which saves setup time when you are switching from one wheel or guard setup to another.

Safety and durability are a real part of the package here, not an afterthought. RAPIDSTOP braking stops most wheels in less than 2 seconds, which improves control after the trigger work is done. Milwaukee also includes an electronic clutch for kickback protection and overload protection to help maximize motor life. The removable dust screen is another practical feature because grinders live in abrasive environments. Keeping dust and metal fines out of the tool goes a long way toward long-term durability.

As an M18 tool, this grinder is compatible with all Milwaukee M18 batteries. Milwaukee specifically calls out the M18 REDLITHIUM FORGE XC8.0 battery as a strong pairing when you want output comparable to a HIGH OUTPUT HD12.0 in a smaller pack. The 5/8 inch-11 spindle also matters because it works with common grinding accessories, and the 4-1/2 inch to 6 inch wheel capacity gives you flexibility for both grinding and cutoff setups depending on the task.

This grinder makes the most sense for metalworkers, welders, general contractors, maintenance crews, and serious DIY users who need a real cordless grinder for more than the occasional quick cut. If your work regularly involves steel, rebar, pipe, plate, or general fabrication, the Milwaukee 3671-20 M18 FUEL 4-1/2"-6" Braking Grinder Slide Switch is built for that level of use. If you only need a grinder once in a while for light cleanup, it may be more tool than you need. But if you earn money with a grinder, the faster brake, broad wheel compatibility, and M18 platform support make a strong case.

Milwaukee 3671-20 M18 FUEL 4-1/2"-6" Braking Grinder Slide Switch

This is the kind of cordless grinder that makes sense for guys who actually lean on a grinder all week, not just keep one around for the occasional quick cut.

• Who it's for: Pros and serious DIY users doing metal cutting, grinding, fabrication, rebar work, and general jobsite cleanup on the M18 platform.
• Why it stands out: You are getting 13 amp corded power claims, a 9,000 RPM brushless motor, fast RAPIDSTOP braking, and 4-1/2 inch to 6 inch accessory flexibility in one cordless package.
• Worth knowing: This is a bare tool, so plan on supplying your own M18 battery and charger. If you want the best performance, do not cheap out on the battery pairing.

• What battery platform does this grinder use? It is part of the Milwaukee M18 system and is compatible with all M18 batteries.
• What size wheels can it run? This grinder accepts 4-1/2 inch through 6 inch accessories.
• What spindle thread does it use? It uses a 5/8 inch-11 spindle, which fits common grinder accessories.
• How fast does the brake stop the wheel? Milwaukee states the RAPIDSTOP brake stops most wheels in less than 2 seconds.