Roloc is a type of attachment, but there are different things you can put on a Roloc arbor. For example, these both attach to a Roloc arbor...
...but these are quite obviously two different abrasives, depending on what you’re trying to accomplish. On the left is a Scotchbrite pad, and they come in varying coarsenesses and colors, while on the right is a 60 grit grinding disc:
Both Roloc, but obviously very different.
Tony, if you want to avoid the confusion you’re getting, you need to be more specific about what you want.
I like purple 3m strip wheels and 3m cubitron2 roloc disc. They're expensive but last so much longer and work better then the cheap stuff I've used. I learned of them courtesy of a rktpwrd thread. I finally found them locally too in 3in and 4in. I put them on my 2 in roloc arbor. I haven't tried on undercoating but I imagine they work. I also ordered orange norton bear tex strip wheels yesterday to try because a member recommends them.
I also bought this today for 25$, just to try on my underbody and rear wheel wells. The snap on version works so Im thinking with a heat gun it'll come off.
whatever type of abrasive you're currently using is fine for what your doing.weld prep and general substrate removal the grade isn't super important.if you were prepping machined surfaces or something MORE specfic that needed to be just so rough/fine then splitting hairs would be in order.don't let this hold you up,run what you've been using and press on.