Very plain but effective neck roller.
Made the cylindrical part from TPU and the core from PLA.
Printed it with High Speed TPU.
If you print the cylinder in one part you wont need the core. I added a split cylinder as well, in that case you will need the core.
I included the core in the additional RAW files as a 3MF.
Once all parts are done simply twist it together and it should lock tight and ready to use.
Pretty heavy duty, works on hamstrings too.