This is a mount for a roller switch with dimensions of ~20x6.5x10mm that originally came stock with my Anet A8 that had become surplus when I switched to a board capable of using sensorless homing.

When building my Rook Mk1 (https://www.printables.com/model/387431-rook-mk1-3d-printer) I needed a Z-axis limit switch and this was what I had on hand.

The mount should be attached to the Rook Mk1 next to the Z-axis motor on the right using M3 screws before inserting the roller switch into the mount. If the roller switch is placed into the mount before attaching to the Rook's frame it will be impossible to insert the M3 screws for attaching to the frame.