Well, folks, after years of wondering about this, I at long last have the answer to my question:
NORTRONICS Macintosh 3.5" Head Cleaning Kit
http://cgi.ebay.com/Macintosh-128K-Nortronics-3-5-Drive-Head-Cleaning-Kit-/140458436044
Scroll down that EBAY listing and note the photo of the two cleaning disks included in that kit, specifically the disk on the left. There's no slot on top, but there is one on the bottom. Aha! The long lost SINGLE-SIDED cleaning kit for 400k drives! And the only kit that could be used on the 400k drives safely. Using normal 800k drive disks (like the disk shown at right in that auction photo) would harm the felt pressure tip that presses down on the drive head.
Feels so good to find the information one has been searching for, for so long.
NORTRONICS Macintosh 3.5" Head Cleaning Kit
http://cgi.ebay.com/Macintosh-128K-Nortronics-3-5-Drive-Head-Cleaning-Kit-/140458436044
Scroll down that EBAY listing and note the photo of the two cleaning disks included in that kit, specifically the disk on the left. There's no slot on top, but there is one on the bottom. Aha! The long lost SINGLE-SIDED cleaning kit for 400k drives! And the only kit that could be used on the 400k drives safely. Using normal 800k drive disks (like the disk shown at right in that auction photo) would harm the felt pressure tip that presses down on the drive head.
Feels so good to find the information one has been searching for, for so long.