The Round Extending Actuator is an extending actuator designed by XYZAidan.
The fabrication process is described in detail on the Instructables page.
The molds are available for download on Thingiverse.
Uses an adapter mold.
From the instructables guide:
Pull the now fully-molded piece of silicone out of the adapter mold. Take the large flathead screwdriver and push it through the opening in order to clear the inside for the tubing. Insert the tubing into the actuator and secure it with the zip-tie.