To simplify things a bit, we have divided our levelers into 4 categories
These type of levelers are solely supported by the bottom shelf of the cabinet, usually held in place by a small grove cut into the sides of the cabinet (see example below) or with some sort of camlock system. In either case this is simply not the strongest support system.
For this reason among others it is necessary to install (4) Levelers onto every single cabinet.
Our front runners all attach and are all supported in the same fashion. They screw into the "sides" of the cabinets but are supported by a lip which is fastened "under" the sides as well. This in our opinion is the ONLY way a cabinet leveling system should be attached.
The sides are load bearing and can hold plenty. (see example below). For this reason among others, we were able to install a "set" of levelers (front/rear) at each "seam" (where the cabinets were joined together). Therefore lowering the overall cost because additional levelers would be redundant.
Attached to "bottom / side" of cabinets
Attached to "inside" of cabinets
Attached to "bottom shelf" of cabinet
Levelers that have no real means of support are the weakest. All the strength of this type of system rely's on those small 1/2" screws.
Shims simply set underneath the cabinet so there is no real load bearing measurement.
However, shims are very unstable and over time they will actually move out of place due to expansion and contraction because they are not attached in any way whatsoever.