# STUB ACME THREAD CALCULATOR FOR ROD AND NUT DIMENSIONS

Stub Acme Thread Calculator to find the dimensions of single start Stub Acme threaded rods and nuts. Only tolerance class 2G is established for general usage in  ASME / ANSI B1.8-1988 and also in the following calculator. If a fit having less backlash is required, the tolerances and allowances for general purpose thread Class 3G or 4G of ASME/ ANSI B1.5 may be used to determine the limiting dimensions for mating threads. Angle of thread of Stub Acme thread is 29°. The thread height is 0.3 times thread pitch. When design requirements necessitate use of a lesser or greater thread height, the data should be obtained from the Appendix of the ASME / ANSI B1.8-1988.

Schematic representation of the thread form of Stub Acme thread is given in the “Definitions” section.

Allowances, Tolerances, and Clearances for Stub Acme Threads

Note: For more information on ANSI standard Stub Acme screw threads including thread designation, basic dimensions, formulas for determining diameters, limiting dimensions and alternative forms , please refer to pages 1991 - 1996 of Machinery's Handbook, 30th.

 INPUT PARAMETERS Nominal diameter (inches) - threads per inch1 1/4-16 5/16-14 3/8-12 7/16-12 1/2-10 5/8-8 3/4-6 7/8-6 1-5 1 1/8-5 1 1/4-5 1 3/8-4 1 1/2-4 1 3/4-4 2-4 2 1/4-3 2 1/2-3 2 3/4-3 3-2 3 1/2-2 4-2 4 1/2-2 5-2 Thread Tolerance Class2 2G

Note: 1 Preferred diameters and associated pitches of Stub Acme threads which are recommended in the ASME standard.

Note: 2 Only class 2G is established in ASME/ANSI B1.8-1988.

 RESULTS Parameter Value Designation --- Nominal Diameter [D] --- in Threads per inch [n] --- --- Thread Tolerance --- LIMITS OF SIZES FOR ACME THREADED ROD Maximum Major Diameter [dmax] --- in Minimum Major Diameter [dmin] --- Maximum Pitch Diameter [d2max] --- Minimum Pitch Diameter [d2min] --- Maximum Minor Diameter [d1max] --- Minimum Minor Diameter [d1min] --- LIMITS OF SIZES FOR ACME THREADED NUT Maximum Major Diameter [Dmax] --- in Minimum Major Diameter [Dmin] --- Maximum Pitch Diameter [D2max] --- Minimum Pitch Diameter [D2min] --- Maximum Minor Diameter [D1max] --- Minimum Minor Diameter [D1min] --- BASIC DIMENSIONS Basic Major Diameter [D] --- in Basic Pitch Diameter [D2] --- Basic Minor Diameter [D1] --- Pitch [P] --- Basic Thread Thickness [t] --- Basic Thread Height [h] --- Total Height of Thread [hs] --- Basic Flat at Crest (internal thread) [Fcn] --- Basic Flat at Crest (external thread) [Fcs] --- Basic Flat at Root (internal thread) [Frn] --- Basic Flat at Root (external thread) [Frs] --- Basic Lead Angle [λ] --- Note 1 --

Note 1: d: degree , m: minute.

### Definitions:

Centralizing Acme Threads: The tolerances of major diameter of external and internal threads are tighter with respect to general purpose Acme threads. In case of a lateral force, external and internal threads contact each other at the major diameter of the thread. This helps to keep alignment of the thread axis and prevents wedging.

Design Profile: The shapes of the external and internal threads in which the limits of dimensions are applied. The thread form of Stub Acme Thread is given in the following figure.

Gages for Stub Acme Threads: Gages for Stub acme threads are defined in ASME B1.8 standard. Gage tolerances, gages for Acme threaded rods and nuts including GO/NOT GO thread ring and plug gages and necessary information related with gauging are given in this standard.

Length of Engagement: The tolerances specified in the ASME B1.8-1988 standard are applicable to lengths of engagement not exceeding twice the basic major diameter.

Major Diameter: The maximum diameter of a thread which is diameter of the crest of a male thread or root of a female thread.

Minor Diameter: The minimum diameter of a thread which is diameter of the root of a male thread or crest of a female thread.

Multi Start Acme Thread: Provides fast relative traversing motion with lower mechanical advantage.

Stub Acme Thread: The thread height is less than general purpose and centralizing acme threads. The thread height is 0.3 pitches for Stub Acme thread. In general purpose form this is 0.5 pitches. Stub Acme thread form is provided for unusual applications where a coarse-pitch thread of shallow depth is required due to mechanical or metallurgical reasons.

Thread class: A classification system to classify the threads for interchangeability and manufacturability.

 Parameter Equation Pitch P $$P=\frac { 1 }{ n }$$ Basic Pitch Diameter D2 $${ D }_{ 2 }=D-h$$ Basic Minor Diameter D1 $${ D }_{ 1 }=D-2h$$ Thickness at Pitch Line t $$t=\frac { P }{ 2 }$$ Basic Height of Thread h $$h=0.3P$$ Total Height of Thread hs $${ h }_{ s }=h+0.5\times (MDAIT)$$ Basic Flat at Crest (internal thread) Fcn $${ F }_{ cn }=0.4224P$$ Basic Flat at Crest (external thread) Fcs $${ F }_{ cs }=0.4224P-0.259\times (PDAET)$$ Basic Flat at Root (internal thread) Frn $${ F }_{ rn }=0.4224P-0.259\times (MDAIT)$$ Basic Flat at Root (external thread) Frs $${ F }_{ rs }=0.4224P-0.259\times (MDAET-PDAET)$$