Mounting screws are included with your unit. The screws are self tapping and will screw into almost all materials, except for stone, tile or granite (you may have to pre-drill for a metal shelf).
The screws extend through the base .375" (3/8"). Most cabinets and shelves are at least 1/2" and usually 3/4" thick. The mounting screw should not protrude through the shelf.
If you decide to remove and move your units, the remaining holes are small and not very noticeable. A little rub of the old hole will smooth it out.