Also, if this site just gives you a server error, that means you're outside its intended service area, apparently...
If you had single sided disks for an Apple ][, and wanted to make them flippy, then you punched another notch, and hole, and then formatted it 4 times, and then cleaned your recording head. Make a whole bunch of them.
Ill get back to you about the DEC floppies.
AFAIR I only hat to put a bit of duct tape over that silly extra hole to make a proper (Amiga) 880KiB DD (Double Density) out of those weird "PC" HD (High Density) disks… — oh wait… I think I went the other way around than you! :-)