Needing advice about angle grinders...

[Frank S]

One thing to seriously look at when choosing an angle grinder regardless of size is the maximum amperage draw it can handle.
Most of the 4" 100 mm grinders will only have a 10 mm arbor their amp draw will range from 5.5 to 7 amps
the most popular small sized grinder being the 4 1/2" 115 MM will have the 5/8-11 arbor the body size is usually near the same as the 4" and the amp draw will range from 6 to 11 amps the switches on all 4 and 4 1/2 " grinders can be an issue since there are so many designs to choose from some are slide where you hold the switch by your thumb some are paddle where you hold the switch with the tips of your fingers some are flip that once on they stay on until you turn them off Rarely will a grinder in this size range have a handle and trigger like the much larger 7 & 9" grinders have.
5 inch grinders can be a mixed bag of mostly over rated 4 1/2" to mid sized grinders shaped more like the larger 7&9" I like the 5 " because mostly I can get them with trigger switches and I am gripping a handle instead of the motor body but they are heavier and you will most of the time want to use both hands to control one
their amp range can be from 7 to 12 amps.
now comes the oddball 6" grinder which is really just a 5 inch with a larger guard but often they will be low RPM less than 3000 making them ore of a polisher than a grinder. 8 to 12 amps
7 Inch grinders are more popular than the 9" their weight is usually slightly less and they can be less bulky their amps can be from 9 to 15 amps consumer grades will have smaller bodies usually
The Kings of the grinding world being the 9" monsters as some call them but not all are huge AEG used to make one though that had a 19 amp draw and weighed 25 lbs it turned 5,500 RPM and you could force your full weight on it and not bog it down but if the disk got hung up it would throw you across the room like a 3/4" drill motor would do with a 1" pipe handle
Bosh makes a 9" that is in my opinion actually a 7" with a 9" guard but it has a respectable 17 amp max draw and will last through years of abuse.
Some grinders have a handle that can be rotated 90° in either direction I have a 7" Ridgid with that feature quite handy at times and the grinder is a little better than middle of the road quality