Asus 1U Rackmount Chassis Kit R10-A2P4 - Manual (Page 18)

Chapter 2: Hardware setup 2-6
2.3.2 Placement direction and screw holes
Align the holes on the motherboard (indicated by white circles in the
picture below) to the corresponding standoffs on the motherboard metal
plate inside the chassis.
Place screws through the designated holes to secure the motherboard to
the chassis. Refer to the motherboard user guide for the specific number
of screws that you need to use.
Place this side (with I/O ports)
to the rear side of the chassis
The following figure shows the specific locations of the standoffs (indicated
by black circles) inside the chassis. These standoffs should match with the
holes on the motherboard as pointed out above.