The difference might be in the details!
Some of these keyboard have
stabilizers underneath them.
In the T400/R400 HMM they are not mentioned anywhere !
In the T500/W500 HMM they are mentioned under "Miscellaneous parts" as part of package 45N5500
In the R500 HMM they are also not mentioned anywhere.
There are 4 sets of parts depending on 14" or 15" chassis and whether integrated or hybrid/switchable graphics.
These make use of existing screws and tapped holes in the rollcage for mounting.
As such, they can be retrofitted to existing systems, but you need to be careful in how these are installed to ensure proper routing of wires, etc.
45N5365 T400 KBD support bracket for Integ model, 2 pieces
45N5366 T400 KBD support bracket for Hybrid model, 2 pieces
45N5367 T/W500 KBD support bracket for Integ model, 2 pieces
45N5368 T/W500 KBD support bracket for Hybrid model, 2 pieces
Don't know (and never tried) if these are also supposed to fit in the R400 and R500.
For some more info:
viewtopic.php?t=75541 (from
15 years ago...)