Well, the ones that attach to the sides are called sidemounts, not undermounts (no, I don't mean to be a smartypants). You'll have to give up space somewhere for glides, whether under or side mount. I'm not sure about the specific measurements though.

Are these framed? I was able to get my cabinet guy to reduce the frame a good deal for less wasted space.

They are frameless cabinets. I know they mount to the underside of the drawer box (as opposed to side mounts that mount to the side), but for some reason I thought in my last kitchen that the undermounts mounted to the sides of the cabinet box rather than to something underneath.

I found an installation guide online that said the Blum ones mount to the cabinet sides. Is that true for all Blum's or only some of them?

Our undermount Blum glides attach to the sides of the cabinet. They are called undermount because they attach under the drawer.

Undermount glides attached to cabinet sides:

Drawers and pullouts installed with the glides underneath:

Cloud Swift - Thank you VERY much for those pictures! That is exactly how I thought they attached. I can't figure out why my cabinet maker is telling me there have to be shelves below each set of glides for them to attach to. I wonder if they add those to increase stability of the cabinet??? And if so, then I certainly don't need them below every single drawer in a 4-drawer bank! Thanks!

Mine cabinets are very stable and they don't have shelves across the insides as you can see.

he's thinking like I was thinking... I'm new to this and he shouldn't be! lol!

i was thinking there would be a wood base below each drawer. could be I got that from the very old dressers and chests i have. they all have a wood base they slide in over.