The dummy hub can be used whenever the back wheel is removed, either for transportation or for chain cleaning. The through axle clamps the device in place and the idler wheel keeps the chain tensioned.

Depending on your hub width, either use the 142 (Road Disc) or 148 (MTB boost) adapter along with the idler wheel assembly. The clip is used to keep the spare adapter in place when the tool is being stored.

UPDATE: (V2) Added new spindle with cut down outer thread in case fit is too tight with standard one
UPDATE: (v3) Reduced adapters and spindle end diameter by 1mm to provide more clearance to drop outs

UPDATE: Added front dummy hubs for through axle road and boost MTB. I use these when transporting the bike with the front wheel removed.

Creality

Ender 3

No

Yes

200

20

Print the adapters vertically with thread at top. Use supports to build plate or tree supports everywhere if the thread needs support too. Idler wheel works well with tree supports.