# ACME THREAD PROFILE FORMULAS

ACME thread profile, form and formula for General purpose ACME screw thread.

ACME Screw Thread Profile

D = basic major diameter, internal thread D1 = basic minor diameter, internal thread D2 = basic pitch diameter, internal thread d = basic major diameter, external thread d1 = basic minor diameter, external thread d2 = basic pitch diameter, external thread P = pitch h = basic thread height

General Purpose ACME Thread Form

Stub ACME Thread Form

### General Purpose ACME Thread Formula

 Parameter Equation Pitch (P) $$P=\frac { 1 }{ n }$$ Basic Pitch Diameter (D2) $${ D }_{ 2 }=D-0.5P$$ Basic Minor Diameter (D1) $${ D }_{ 1 }=D-P$$ Thickness at Pitch Line (t) $$t=\frac { P }{ 2 }$$ Basic Height of Thread (h) $$h=\frac { P }{ 2 }$$ Basic Flat at Crest (internal thread) (Fcn) $${ F }_{ cm }=0.3707P$$ Basic Flat at Crest (external thread) (Fcs) $${ F }_{ cs }=0.3707P-0.259\times (PDAET)$$ Basic Flat at Root (internal thread) (Frn) $${ F }_{ rn }=0.3707P-0.259\times (MDAIT)$$ Basic Flat at Root (external thread) (Frs) $${ F }_{ rs }=0.3707P-0.259\times (MDAET-PDAET)$$ Minimum Stress Area (At) $${ A }_{ t }=3.1416{ (\frac { { d }_{ 1min }+{ d }_{ 2min } }{ 4 } ) }^{ 2 }$$ Minimum Shear Area per Unit Length (As) $${ A }_{ s }=3.1416\cdot { D }_{ 1max }\cdot (0.5+n\cdot \tan { { 14.5 }^{ ° }\cdot ({ d }_{ 2min }-{ D }_{ 1max }) } )$$

PDAET - Pitch diameter allowance on external thread, MDAIT - Major diameter allowance on internal thread, MDAET - Minor diameter allowance on external thread

### Stub ACME Thread Formula

 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 $${ F }_{ rs }=0.4224P-0.259\times (MDAET-PDAET)$$

PDAET - Pitch diameter allowance on external thread, MDAIT - Major diameter allowance on internal thread, MDAET - Minor diameter allowance on external thread

### Reference:

• Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) . Machinery's Handbook . 30th edition.  Industrial Press Inc.
• Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2012) . Machinery's Handbook . 29th edition.  Industrial Press Inc.
• ASME B1.5-1997, ACME Screw Threads