Lead Screw Linear Actuators – External, Captive & Non-Captive

Motorized lead screw linear actuator assemblies use a threaded rod and correspondingly threaded nut to convert rotary motion into linear motion. The screw and nut threads are often coated with PTFE to reduce friction and prevent flaking. These systems are typically driven by NEMA frame stepper motors in sizes 11, 14, 17, and 23. PBC Linear manufactures conventional external lead screw systems as well as integrated captive and non-captive internal actuator designs.

In external linear actuator configurations, the nut is external to the motor assembly while the motor rotates the lead screw to move the attached load. In this arrangement, the screw rotates while remaining fixed in position and is supported by external mounts, couplers, or guide hardware.

In captive linear actuators, where the nut is internal to the motor assembly, one end of the lead screw is retained within the motor so the screw cannot rotate, while the motor drives an internal threaded mechanism that forces the screw to extend and retract linearly from the motor body. Because part of the screw must always remain engaged inside the actuator, captive designs normally travel short distances of approximately 2 to 12 inches (50 to 300 mm) and up to approximately 20 inches (500 mm) with a larger diameter screw.

In non-captive linear actuators, where the nut is also internal to the motor assembly, the lead screw passes completely through the motor instead of being retained within it. This allows substantially longer travel lengths and more flexible mounting arrangements. In one common configuration, the screw rotates, forcing the motor and attached load to travel linearly along it, and this is the recommended arrangement from PBC Linear. In another configuration, the motor remains stationary while the lead screw both rotates and moves linearly through the motor. Standard non-captive lead screw assemblies are available in lengths up to approximately 72 inches (1,830 mm).

Stepper motor control allows travel direction to be reversed while enabling repeatable motion cycles with precise control over position, speed, and timing. Non-captive actuator systems are often paired with linear guides to improve rigidity, alignment, and overall load capacity in robotics, automation equipment, CNC machinery, and industrial positioning systems.

External and both captive and non-captive configurations deliver high thrust, precise positioning, and long service life. Each actuator incorporates angular contact bearings within the motor housing to fully support the lead screw. Larger, preloaded bearings increase thrust capacity, improve durability, minimize runout, and eliminate axial play—ensuring consistent precision and repeatability over time. Optional Smart Motor Technology delivers up to 50% more torque, significantly reducing cycle times and improving overall machine efficiency.

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