Model#: MILN2781-20

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Brand new items;Full manufacturer warranty available
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New items with possible minor cosmetic damage; CPO 120 day money back guarantee
Returned items inspected, repaired and tested by CPO technicians; CPO 60 day money back guarantee

Milwaukee 2781-20 M18 FUEL Lithium-Ion 4-1/2 in. - 5 in. Slide Switch Grinder with Lock-On (Tool Only)

  • Note: Battery & Charger sold separately
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Product Overview


The M18 FUEL 4-1/2 in. / 5 in. Slide Switch Grinder supplies maximum sustained power to complete the toughest grinding, surface preparation and cutting applications. The POWERSTATE Brushless Motor provides up to 10X longer motor life and lower cost of ownership. The M18 REDLITHIUM XC4.0 Battery Pack (Sold Seperately) delivers up to 4X more run time and 20% more power. The grinder features REDLINK PLUS Intelligence, the most advanced system of cordless power tool electronics, for maximum performance.
  • POWER TO GRIND means the World's first cordless grinder with corded performance
  • Same metal housing and gearing system as legendary high performance corded grinders
  • Thin body design and anti-vibration handle provides optimized balance to rest easily in your hands
  • Tool-free accessory changes and guard adjustments mean less downtime during work
  • POWERSTATE Brushless Motor delivers maximum power and up to 10X longer motor life
  • REDLINK PLUS Intelligence provides optimized performance, electronic clutch, and overload protection using total system communication between tool, battery and charger
  • REDLITHIUM XC 4.0 Battery Pack (Sold Separately) provides superior pack construction, electronics, and performance to deliver 2X more run-time and more work over pack life
  • M18 FUEL 4-1/2 in. - 5 in. Slide Switch Grinder with Lock-On (Tool Only) -2781-20
  • Flange Nuts
  • Wheel Guard
  • Spanner Wrench
  • Tool Only - Batteries and Charger Sold Separately


Series: FUEL
Cordless: Yes
Length: 15 in.
Width: 3.27 in.
Height: 8.58 in.
Weight: 5.8 lbs.
Arbor Size: 5/8 in - 11
Batteries Included: 0
Battery System: M18
Battery Type: Li-Ion
Bluetooth Compatibility: No
CSA Safety: Yes
Case Included: No
Charger Included: No
ETL Safety: Yes
Motor Type: Brushless
No-Load Speed (RPM): 8500
Powered Tool Power Source: Electric - Cordless
Spindle Thread: 5/8 in - 11
Switch Settings: Lock-On
Switch Type: Body grip/slide
UL Safety: Yes
Variable Speed: No
Voltage: 18V
Wheel Diameter: 4.5 in / 5 in
Wifi compatibility: No



4.8 / 5.0
84 Reviews
5 Stars
4 Stars
3 Stars
2 Stars
1 Star
Yes, I would recommend this to a friend (21)
Powerful (16)
Easy To Use (14)
Ergonomic Design (11)
Value (5)
Heavy (1)
Uncomfortable to Use (1)
Best Uses
Jobsite (8)
Frequent Use (6)
Large Projects (5)
Small Projects (5)
I am very impressed with my grinder !
I use my grinder for several light duty grinding and cutting jobs where power isn't handy to get at !
August 26, 2019
Originally posted at
Great product!
Love Milwaukee tools! Very dependable. And power is there when I need it.
August 18, 2019
Originally posted at
I use it on semi truck and fabricating brackets PTOs ,fenders and toolboxes it works well for cutting and grinding welds and different metals. The battery lasts very long and it’s nice that you don’t have A cord getting in your way.
August 18, 2019
Originally posted at
Best gift ever
I got my husband the Milwaukee 4 1/2 inch grinder for Christmas and he is amazed how much power it has. Normally he would use a corded grinder over a cordless, simply because they have much more power but that's not the case here. He now tosses the corded grinders to the side and chooses to use Milwaukee's cordless tools over any tool out there!! Thanks Milwaukee!!
August 17, 2019
Originally posted at
Excellent buy
I prefer the lock-on feature when I’m using a cutting wheel for cutting steel siding.
August 16, 2019
Originally posted at
I would buy this product again and again
I've used it on commercial jobs weekly. cutting pipe, cutting rebar, cutting concrete. I've used it at home several times with flap discs for sanding. Its awesome works great, I do wish it had 15A corded power. Its limited in power I believe for safety
August 15, 2019
Originally posted at
I wouldn’t hesitate a minute to buy again
Just bought it and already used it quite a bit. I’m a welder by trade and fabricator on a daily basis that has to work in heights . When working on top of catwalk, silos or towers, it’s not easy. Majority of time there is no electricity available, so you need battery operated tools. You can’t go wrong with Milwaukee tools. Well fabricated, rugged and batteries that lasts.....very impressed with this grinder, Bring a couple of batteries up with me and good until lunch. Love this grinder
August 14, 2019
Originally posted at
I wouldn’t buy this model again
It’s a great grinder but it never stays on, you have to hold to switch the whole time you grind. I recommend the grinder, but don’t buy the one with the switch on the top.
August 14, 2019
Originally posted at
Grinder works amazing
I grind metal in peculiar positions and this grinder is perfect for that. Especially not having to worry about a power cord!
August 13, 2019
Originally posted at
great tool
The grinder has plenty of power equal to my corded grinder. The tool is slightly heavier than my corded grinder partly because of the battery. Way handier than a corded grinder, can use it anywhere. only negative is battery useage, I go thru a 5ah battery pretty fast when I am wire brushing metal before painting, but I have two batteries so it is not a big deal. Very glad I got the slide switch, don't like paddle switches.
August 13, 2019
Originally posted at

Questions & Answers

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Browse 3 questions Browse 3 questions and 6 answers
How long can be used before recharge in production no stop ?
Edwin on Apr 19, 2016
BEST ANSWER: That is a very difficult question to answer, runtime depends on many variables. Without knowing whats being done with the grinder, continous runtime could be anywhere from 30 minutes to a couple hours with the 4Ah battery. Keep in mind, charge time is relatively short, with a couple of batteries you can get alot accomplished with little
The description states "Tool-free accessory changes," but a reviewer said that he needed a tool to remove the flange nut. The downloadable manual also states that a spanner wrench is required to tighten and loosen the flange nut. Also, if accessories can be changed without a tool/wrench, why is one included? Can wheels/accessories be installed and removed without a tool or not?
A shopper on Nov 25, 2017
BEST ANSWER: In almost all cases, you can swap blades without a tool. If the blade is the face, on the back of the head is a lever which unclamps the spindle. It is not enough to flip this lever up; you must flip it all the way forward. When you do, the spindle/arbor tension is released and you can unscrew the spindle-cap/arbor-nut with your fingers. If you don't understand how this works, you will probably overtighten the cap/nut and then need a wrench to get it off again.

So, wheels/accessories CAN be installed without a tool, if you don't go out of your way to make it more difficult than necessary.
Can you interchange the types of Milwaukee batteries with chargers and tools?
Frank on Oct 19, 2015
BEST ANSWER: All Milwaukee 18 volt lithium ion tools and batteries are compatible,so yes everything is interchangeable.

New Vs. Reconditioned

What's the difference between New and Factory-Reconditioned?

Factory-Reconditioned products have been returned to the manufacturer and are restored to like-new operating condition; they go through a rigorous testing and inspection process. Plus, they offer a significant savings vs. new.
  • Reconditioned products may have minor cosmetic blemishes or scratches that do not affect item performance.
  • Reconditioned products may not come with all of the consumables the new version comes with (bits, sanding pads/papers, cases, etc.).
  • Both come with a manufacturer warranty and are covered by our Money Back Guarantee; New is 30 days, Reconditioned is 120 days.
Condition: New Factory Reconditioned
Features: Same Same
Specs: Same Same
Includes: M18 FUEL 4-1/2 in. - 5 in. Slide Switch Grinder with Lock-On (Tool Only) -2781-20,
Flange Nuts,
Wheel Guard,
Spanner Wrench,
Tool Only - Batteries and Charger Sold Separately
M18 FUEL 4-1/2 in. - 5 in. Slide Switch Grinder with Lock-On (Tool Only) -2781-80,
Flange Nuts,
Wheel Guard,
Spanner Wrench,
Tool Only - Batteries and Charger Sold Separately
Availability: In Stock Out of Stock
Warranty: 5 Year 1 Year