EDIT CORRECTIONS: For 103 key Model M’s Left and Right Alt Key’s are the same size’s as each other (1.5U)
I am having trouble finding a good reference on the exact keys that will work with the model M.
Can someone confirm if I have this correct on a regular Model M?
- 1U – Most of the keys are this size
- 1.25U – The smaller Alt key (Correction: May only apply for Mini M’s)
- 1.5U – The bigger Alt key, and also the Left and Right Clt, Tab key, and Backslash
- 1.75U – Caps Lock (only key this size)
- 2U – Backspace and Numpad Zero Key
- 2U V – Numpad’s Enter key and the Plus key above it.
- 2.25U – Left Shift and Enter Key
- 2.75U – Long shift key (only key this size)
Thank you in advance.

Yes, sorry you are correct. on a REGULAR full sized model M they both are 1.5U’s. I was using one of the new Mini M’s when I was figuring it out, and it looks like the Mini M is using a smaller alt for the right side. And my 103 key model M appears to have both Alt’s as 1.5U Thanks again!