A couple things,
While thin pads work best for DA Polishers like the PC, Griot's and Meguiar's, that's not a factor when it comes to gear driven tools.
This is just my opinion but the best pads on the market right now for the Flex 3401 are the 5" Hybrid Pads.
The face of these pads equals 5" in diameter and the design has them tapering down to the Velcro backing which is 4" and fits the 4" backing plate perfectly.
For doing major correction work, get the Blue Foamed Hybrid Pad, this thing is dang near indestructible and with a good compound will remove defects incredibly fast.
For less aggressive cutting action get either of the cutting pads and for sure get the white polishing pad and the black finishing pad.
The smaller size of the face of the pad does two things, 1.
Makes the tool incredibly easy to control. You still want to practice holding the pad flat but the smaller size makes operation easy. 2.
Fits the thin panels common to new cars better than larger pads.
I have an article on this and you can find it in my article list
in the section dedicated to the Flex 3401, it's easy to find, just click to my article list from the link in my Signature Line which is in ALL my posts and the scroll down till you see this picture, Flex 3401 Forced Rotation Dual Action Polisher NEW
- New 5" pads for 4" Backing Plate on Flex 3401
And here's the article showing these pads... 5" Hybrid Pads for the 4" backing plate on the Flex 3401!
These new pads are not in stock yet but you can get a glimpse of them in action below.... Live Broadcast Video - 1965 Plymouth Valiant - Extreme Makeover ***Live Broadcast Video - Extreme Makeover - 1965 Plymouth Valiant*** Here's some still pictures I took from the Valiant Extreme Makeover with Justin using them...
These pads really work well with this tool. If you don't have the 4" backing plate then ANY of the 6.5" pads from Lake Country work GREAT on it to as do the Meguiar's 7" Softbuff pads.
The larger size pads work great for tackling larger flat panels.