I discovered by accident that they fit, when one popped off my PC keyboard after hitting it in a moment of anger, so I had to try. I even have keys that will fit the outer function keys on either side of the Qwerty keys, though since the key posts are off-center on the 800, they would need considerable re-working and it would probably be easier to just print proper ones. They are just from a cheap $10 keyboard, and after a bit of research, I found I had 2 black and one white cheap USB PC keyboards with keys that have square plungers the same size as the 800. I've already decided I'm most likely not going to use these keycaps, as it's too far removed, I think, from the unique look of the 800 and the mock-up IBM 'ATARI' PC. But I thought I'd show you guys what an 800 with low-profile keys would look like... By the way, I also discovered that the key caps from my old salvage 600XL also have square posts that fit perfectly in the 800's plunger shafts and they sit exactly as low-profile on the keyboard as the PC key-caps. So if I decide to have lower-profile keys on my 800 that I will use the 600XL keycaps are are of far better quality than the PC ones. The one advantage to using the 600XL key caps on my custom 800 (besides low-profile, if that can be considered an advantage, seems more like personal taste) is that I would be saving the 800 keys caps in case I ever wanted to change it back to stock-looking; all I'd need is to re-paint the case in beige. Though it's highly doubtful that I'd ever want to do that, as if I had any doubts at all I wouldn't be doing it in the first place and I'd probably just get another 800 to keep stock. Of course the 600XL key caps don't have off-center plungers spots like the 800, so the outer function keys would still have to be modified.