Inserts for the second hole of an HD floppy to turn it into a DD floppy.
This is basically just a cube with the correct dimensions to fit into that hole.
1) Use electrical tape to tape up one side of the disk. Leave enough tape to wrap it around later.
2) Put the insert into the hole
3) Wrap the rest of the tape around to the other side

This solves the problem that, if you only use tape and no insert, the switch in the floppy drive will press the tape a little inwards (into the hole) eventually, so the detection of the disk as DD might be unreliable.

Creality

Ender-3 V3 SE

No

No

0.12mm

solid