Slotted bases intended to mate to standard 1/2" post holders for mounting optics and or detectors to optical tables. The slots in the base are sized for clearance to slide along 1/4-20 screws. You should use a washer to distribute the load when tightening down to the table to increase the life of the part.

The center hole(s) are countersunk and required a 1/4-20 screw up through the bottom to attach to commercially available post holders. I've successfully printed both of these versions in PLA.

You may find you need to widen the center through holes depending on any shrinkage during the print.