The acme thread form has a 29-degree thread angle with a flat valley and a thread height equal to half the distance between each valley and thread. The acme thread was developed as a strength improvement on the square thread and is useful for high-load work.
AMESweb.info has a calculator useful for determining the necessary dimensions of an acme threaded screw based on number of threads per inch, thread weight tolerance, and the number of thread starts. For Acme screws, there are three primary tolerance classes: 2G, 3G and 4G. EngineersEdge.com provides an additional diagram showing the basic acme thread specification.