You can extend / retract by turning one part against the other.
Make sure the cable is not tightly wound to reduce fatigue on the conductors in the cable.
Technical
2 parts just clip together. Comes in 3 sizes L, M, S.
Printed with faces down using ABS.
I'm really new to 3D i have downloaded the lubricant Jar. Extremely useful as i found out the rails need attention often. i absolutely love it. I hope i can get this good at design. I haven't found a 3D program i can make something of my own. But i will keep at it.