The Reverse Circulation 4in Saver Sub is used to connect the entry side swivel to the first piece of RC drill pipe and is attached to every pipe, going in and coming out. This position in the string is subject to much wear, so saver sub was designed to be an inexpensive, easily replaceable part. As such, it is used to protect the threads on the actual pipe and allows for a quick and onsite replacement. Using saver sub offers great advantages, as it is cheaper to change a saver sub often, than to buy new pipe once.
A saver sub is usually located between the first rod and the top drive head , and protects the top drive head threads from the high number of breaks during drilling. It is more economical and productive to wear a saver sub versus the threads on the top drive head.