When I was at the NMRA Convention in Denver in the late 1980's I saw a vendor selling small DC motors which had internally threaded rotors.  The motors did not have shafts but the rotors acted as nuts to threaded rod.  They could accept a threaded rod (example: 1/8") of any length.  When the motor was powered, the threaded rod would move through the motor like a linear actuator.  Limit switches could be used to stop the motor.  The vendor had motors sized for 1/16" to 1/4" threaded rods both standard and fine thread.

I am looking for the name of the manufacturer(s) and/or vendor(s).  I have several project that could use these motors.

Thank you in advance for your help.