More than 100 years ago, in 1894, the Acme thread form came into existence. It quickly became the replacement for the existing square thread screws. It offered advantages the square thread screw did not. Its three variants:
1. General Purpose (G) Thread
2. Centralizing (C) Thread
3. Stub Acme Thread
Quickly became the popular choice.
It owed its acceptance to several characteristics. It is
- Easier to cut through either single-point threading or die
- Wears better than square threads
- Stronger comparatively
- Ensures a smoother engagement of the half nuts on a lathe leadscrew
The stub version has certain qualities in common with the other Acme thread types. It also has its differences.
Stub Acme Thread Qualities
This Acme thread version has the same basic design as general-purpose models. However, it does have a thread depth distinct from the other thread types. It is less than one-half the pitch. The General’s pitch is 0.5 pitches to the Stub’s 0.3 pitches. The stub also has a higher static load capacity but lower dynamic load capacity.
In general, the flank angle is 29 degrees. However, you can find 60° stub threads. These serve a specific purpose, acting as a substitution where the axial leads do not necessitate the lesser flank angle. Modified stub acme threads are also available.
Applications
The Stub form of Acme thread is often reserved for unique applications. It works optimally when the specifications call for a shallow depth (thin wall) and a coarse pitch. The rationale may be mechanical or metallurgical. Examples are tubes for use in thin-walled oil field equipment.
Stub Acme Thread
Acme threads come in different styles or types. The three major variations are the General Purpose, the Centralizing and the stub. Of these three, the stub Acme thread addresses distinctive applications. In general, it is for those situations where the shallow nature of the stub will correctly fulfill the application’s specifications.
