SeeMeCNC Rostock MAX v2 Assembly Manual page 86

Now it's time to attach the Onyx and its mounting plate to the base – grab the round nylon
spacers and the six #4-40 flat head screws that were included with the Onyx.
Fig. 5C-28:Attaching the Onyx & mounting plate.
Orient the Onyx heated bed such that the LED is farthest away from you and near the Z axis.
You can refer to Fig. 5C-29 on the following page for clarification if needed.
Make sure that the Onyx and its mounting plate holes are roughly aligned with the mounting
holes in the top of the base. Slide a nylon spacer under the mounting plate so that it aligns with both
the Onyx and mounting plate holes. Insert a #4-40 flat head screw and tighten it only a turn or two.
You want to leave the screws loose until you've got all six installed.
Rostock MAX v2 Assembly Guide
86