The website mentions the following key points:
The front rack opening must be 451 mm wide ± 0.75 mm (17.75 in. ± 0.03 in.), and the
rail-mounting holes must be 465 mm ± 0.8 mm (18.3 in. ± 0.03 in.) apart on-center
(horizontal width between the vertical columns of holes on the two front-mounting flanges
and on the two rear-mounting flanges). Figure A-3 is a top view that shows the
specification dimensions.
Drawer Rail
Mounting
Flanges
Figure A-3 Top view of rack specification dimensions (not specific to IBM)
571mm (22.50 in.)
Back, No Door
494mm (19.45 in.)
Front, No Door
451mm (17.76 in.)
494mm (19.45 in.)
Appendix A. Server racks and energy management
203mm (8.0 in.)
719mm (28.31 in.)
51mm (2.01 in.)
55