I designed this because I needed more height for the shelf that is attached on my desk (I believe this is a desk from early 2000s. I needed a 1" extension. All you need to do is measure and buy the appropriate length screws to match the additonal space you need with your design.

The holes for the hardware on this are designed for 1/4" wide x 1.5" long screws (think they are 1/4-20 screws for width and thread pitch). I needed a 1" extension, and the original screws were 1/2" long. You can scale this in the Z direction for this desk if you need less space than my 1" design, just make sure you buy the proper length screws.