Upper Cabinet Filler Installation
In this photo, the cabinet installer hung the upper first and is now measuring for the upper cabinet filler size. When using this method you must get the filler to fit really tight in the space so that it will bind in place. The installation will be easier completed this way because there is no room for you to hold the scribe piece in place. Once you have it wedged in nice and flush with the face of the cupboard, you can attach the upper cupboard scribe filler with about three screws.
For more detailed information go here:How To Attach Fillers On To Cabinets