All Acme threads are actually designed on a specific form. They are defined by their pitch and thread angle, which was created to allow smoother movement, less friction and to be easier to manufacture and utilize. Over time, development of different types of Acme thread forms has increased the choices for OEMs.
There are actually three different Acme thread forms. The centralizing and general-purpose thread forms will have a nominal depth that is half of the pitch. In addition, they will have the standard twenty-nine-degree thread angle.
The stub Acme thread differs in the thread depth. Instead of half the pitch for the thread depth, they will have a thread depth of less than a half of the pitch. In general, while both offer strength and durability, the specific design of the stub Acme thread is often the thread form of choice when durability is going to an important consideration.
With 60% of the depth of the general purpose or centralizing Acme threads, they are naturally able to stand up to extreme types of operating conditions. This can include heavier loads, high shock and vibration considerations as in extreme types of uses and applications.
This includes in very long applications. The shorter thread height means that the screw doesn’t have to run perfectly straight and true to provide the even, continual motion.
The stub Acme thread will be classed the same as the other types of Acme thread forms. This allows for ease of ordering as all that will be required in the class designation, which indicates the number of threads per square inch as well as the if the thread is right handed or left handed. This will be designated by RH or LH that will follow behind the number and letter combination that indicates the class.