Leadscrews are a superior replacement to threaded rods

From RepRap Wiki: Threaded Rod

Leadscrews are threaded rods used to lead a component on, for example the X-axis assembly on the Z-axis. For most RepRaps a common (straight!) threaded rod is sufficient, but for higher precision and reduced wobble you might want to use real leadscrews.

There are two main thread profiles for leadscrews, both of which are trapezoidal: Trapezoidal and Acme. The important but subtle difference is the angle of the thread flank. Be sure to get matching nuts.

See also Wikipedia: Leadscrew:

A leadscrew (or lead screw), also known as a power screw1 or translation screw,2 is a screw used as a linkage in a machine, to translate turning motion into linear motion. Because of the large area of sliding contact between their male and female members, screw threads have larger frictional energy losses compared to other linkages. They are not typically used to carry high power, but more for intermittent use in low power actuator and positioner mechanisms. Common applications are linear actuators, machine slides (such as in machine tools), vises, presses, and jacks.3

Leadscrews are manufactured in the same way as other thread forms (they may be rolled, cut, or ground).

There are three types of thread used by leadscrews:

  • Square
  • Buttress
  • Acme

Advantages and disadvantages:

The advantages of a leadscrew are:

  • Large load carrying capability
    • Compact
    • Simple to design
    • Easy to manufacture; no specialized machinery is required
    • Large mechanical advantage
    • Precise and accurate linear motion
    • Smooth, quiet, and low maintenance
    • Minimal number of parts
    • Most are self-locking

The disadvantages are that most are not very efficient. Due to the low efficiency they cannot be used in continuous power transmission applications. They also have a high degree of friction on the threads, which can wear the threads out quickly. For square threads, the nut must be replaced; for trapezoidal threads, a split nut may be used to compensate for the wear.