Threaded rod is measured Diameter-Threading x Length. For example, you may find a threaded rod measuring 1/4"-20 x 6ft. The 1/4" is the rod's diameter, the 20 means there are 20 threads per inch of rod, and the 6ft is how long the rod is. Most threaded rod is available in either three-foot or six-foot lengths. Metric is measured the same way, but instead of threads per inch, it's thread pitch or the distance between each thread. Metric threaded rods are available in lengths of one meter.