You can read up on them over on the ServoCity website. I've seen a similar device used on electric auto antennas.

Here is the LINK

The 12 volt version might need a single H-Bridge in order to be used with the EZB.

I've made my own linear actuator with a standard servo motor that can hook up to the EZ-B. It's all ghetto style, lol.

Linear actuators are one of my favorite components to use for the large scale robots I build. Mechanical interface is easy and they are available in a range of stroke lengths and actuation force/speeds to meet the requirements of your application. I used six 12V linear actuators for my ARMadeus Mk7 project. I controlled all of them with electronic speed controllers just like any brushed dc motor. Sabertooth 2X12s work great and are ideally matched for larger robots. Running the Sabertooth in the serial mode allows 2 linear actuators to be controlled using only one EZ-B port. If you don't need to vary the extend/retract speed an appropriately rated DPDT relay would work fine.

You can make simple yet very strong linear actuators with a few threaded nuts and a long threaded rod that matches those same nuts. You make a mount on one ends of the rod that holds it in place then grease the rod. Thread on nuts to the position desired then get a tube metal or plastic slightly larger than the nut , glue the nut to the inside of the tube. Now the opposite end of the tube attach a servo or other geared motor. When this motor spins the nut inside pushes or pulls the threaded rod.

thanks for the help