Acme Threading

The uses of Acme Threads usually involve special designs requiring individual consideration.

Each tapping job becomes a minor engineering project of its own.

The inherent exactness in application of Acme taps makes close coordination between manufacturer and user particularly important. An example of an Acme Thread application may be aircraft wing flap hydraulic actuators or a simple car bumper jack.

American Standard Acme Threads are used to produce traversing motion in valves and other power transmission mechanisms requiring high strength and free movement over long periods of operation.

American Standard General Purpose Acme Thread: Provides clearance of all points of contact between external and internal surfaces for free movement. Normally these applications are indicated with a Class of Fit symbols of “2G”, “3G”, or “4G”. The numbers 2,3, and 4 will control the amount of backlash allowed. Included flank angle is 29°

American Standard Centralizing Acme Threads: Clearance at pitch and minor diameters, with limited clearance at major diameter so that alignment of screw and nut is controlled. The class of fit symbols here are indicated with “2C”, “3C”, and “4C”. Included flank angle is 29°

Stub Acme are similar to General Purpose Acme but are used where coarse pitch thread of shallow height is required. Included flank angle is 29°

60° Stub Threads: May be substituted where axial leads do not require the smaller flank angle. They are also for applications where shallow thread height is required as on fitting-up bolts and nuts. Included flank angle is 60°.

Modified Square Threads: Used as an equivalent to Square Threads for all practical considerations. However, they should not be used where Acme Threads can serve the same purpose. Modified Square Threads have 10° included flank angles.

Acme thread profile characteristics pose a challenge for internal threading because their block like profile requires that large amounts of material must be cut and removed. Chip load becomes a major factor and the types mentioned are designed to control this.

Taps are furnished in normally two types for most of the above. Sets include either one or two roughers and a finisher. Single pass tandem taps can also be designed with the roughing section built ahead of the finishing section on the same body.