Which clipper does this blade fit?

It is made for the Andis ProClip 5-in-1 Cord/Cordless Clipper. It is not a universal blade and will not fit other Andis clippers or other brands.

What do the 9 to 40 cut lengths mean?

They are the five adjustment positions on the blade, from shortest to longest. They are Andis's own numbering, not standard clipper blade sizes, so judge them by test-cutting rather than by comparing to a #10 or #30 blade.

Can I use my existing attachment combs with it?

Yes. Andis says the blade is compatible with your existing attachment combs, so combs you already use on the ProClip clipper carry over.

Is this a whole clipper or just the blade?

Just the blade. It is a replacement or upgrade part for the ProClip 5-in-1 clipper, which is sold separately.

Is it good for thick or matted coats?

Andis claims extra-strength cutting that resists snagging in dense or textured areas. It is still a blade, so heavily matted coats should be worked out before clipping.

Do I need to oil or maintain it?

Treat it like any clipper blade: keep it clean and oiled between uses. Andis does not publish a replacement interval, so replace it when cuts start pulling.