When you put a material onto the Replicator's print bed to print onto, such as glass or wood, you need to adjust for that thickness. The springs are only adjustable by a small amount, and when you move then you have to re-level. By putting a clip of a given thickness on the back of the print bed, where it touches the Z limit switch, you cause the bed to stop that much lower, leaving room for the glass, wood, etc.

One nice property is that you can add and remove glass, and swap the adjuster, and not have to re-level the print bed.
The original idea is from the parent Thing, but this is an original implementation.

If you want to lower the platform by 1mm or 5mm, you can use the attached STL files.

Otherwise, click 'Customize' and enter the thickness of the material you're adding to the bed, and print away.

Slide the clip behind the print bed, onto the top of the part of the platform where the switch hits.