Plug/Cover to block debris from getting inside the hole at the bottom of the rail for the bed.
Was just looking to grab a hair more clearance so I trimmed 1.25mm off the top of the model to make it slightly thinner (2mm vs 0.75mm, you can see the difference in the second picture). Credit to clselee.tw for the great model!
*Note: When the bed is fully in the bottom position the bearings on the rails slide in to these holes, so just make mental note to remove them if you plan to print with the full range of the Z axis
Looking for more covers to clean things up, check out some of my others!