ACME THREAD PROFILE FORMULAS

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

Acme Thread Calculator Tolerances

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

General Purpose ACME Thread Form

Stub 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

Supplements:

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