The World of ACME Screw Threads

In my younger days I thought ACME was the name of a company that brought Wile E Coyote the newest innovations on how to catch a Roadrunner, but as I have grown older I realize ACME is an important screw thread found in daily use in many places.

The word ACME as defined by Merriam-Webster is: the highest point or stage; or: one that represents perfection of the thing expressed. So if we take the definition for what it is, when it comes to screw threads, ACME screw threads are the best thing going. When formulated in the mid 1890's, ACME screw threads were intended to replace square screw threads, and a variety of other screw threads forms, used mainly for the purpose of producing traversing motions on machines, tools, etc. ACME screw threads are now extensively used for a variety of purposes. The problem is that it can be a pretty confusing screw thread to deal with if you're not sure what you're looking at. I hope to clear it up for you here.

There are 3 different forms of ACME Screw Thread: General Purpose ACME, Centralizing ACME, and Stub ACME. General Purpose ACME Screw Threads and Centralizing ACME Screw Threads are defined in ANSI B1.5 while Stub ACME Screw Threads are defined in ANSI B1.8. While the three different variations of the ACME screw thread are not all listed in the same standard they do share some similar characteristics. All three styles of ACME screw threads have 29° included angle; all are perceived as a bilateral transverse motion screw thread; all offer high strength with ease of machining and assembly; and all are largely used for feed and adjusting screws.

To add just a little more confusion we will briefly tell you about the Trapezoidal screw thread (the Tr-series). The Trapezoidal screw thread is sometimes called: Metric ACME; European ACME; German ACME. None of these designations is proper nor accepted by the standards (DIN 103; DIN 38; DIN 263; DIN 30295; DIN 6063). The Trapezoidal screw thread is very similar to the ACME screw thread. The two screw thread forms are visually identical, used in similar applications, and only through careful measurement will you find the differences. Trapezoidal screw thread has a 30° included angle where ACME screw thread has 29° included angle. Trapezoidal screw thread is made and measured in millimeters where the ACME screw thread is made and measured in inches. Trapezoidal screw thread pitch is stated in millimeters of pitch where ACME screw thread pitch is stated in threads-per-inch.

Originally Posted: 12/9/2008
Last Revised: 4/14/2011
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