Involute Spline Names, Symbols, and Relations for ANSI Metric Standard

Term	Symbol	Formula
Term	Symbol	30 deg Flat Root 0.5 to 10 module	30 deg Fillet Root 0.5 to 10 module	37.5 deg Fillet Root 0.5 to 10 module	45 deg Fillet Root 0.5 to 10 module
Pitch diameter	_D	mZ
Base diameter	DB	mZ cos α_D
Circular Pitch	p	πm
Base Pitch	p_b	πm cos α_D
Tooth Thick Mod	es	According to selected fit class, H/h, H/f, H/e, or H/d
Min Major Diameter Int	DEI min	m(Z +1.5)	m(Z +1.8)	m(Z +1.4)	m(Z +1.2)
Max Major Diameter Int	DEI max	DEI min + (T + λ)/tan α_D
Form Diameter Int	DFI min	m(Z + 1) + 2c_F	m(Z + 1) + 2c_F	m(Z + 0.9) + 2c_F	m(Z + 0.8) + 2c_F
Min Minor Diameter Int	DII min	DFE + 2c_F
Max Minor Diameter Int	DII max	DII min + (0.2m^0.667- 0.01m^-0.5)
Circ Space Width Basic Min Effective Max Actual Min Actual Max Effective	E_bsc EV min E max E min Ev max	0.5πm 0.5πm EV min + (T + λ) EV min+ l E max - λ
Max Major Diameter Ext^d	DEE max	m(Z + 1) - es/tan α_D	m(Z + 1) - es/tan α_D	m(Z + 0.9) - es/tan α_D	m(Z + 0.8) - es/tan α_D
Min Minor Diameter xt	DEE min	DEE max - (0.2m^0.667- 0.01m^-0.5)²
Form Diameter External	DFE
Max Minor Diameter Ext^d	DIE max	m(Z - 1.5) - es/tan α_D	m(Z - 1.8) - es/tan α_D	m(Z - 1.4) - es/tan α_D	m(Z - 1.2) - es/tan α_D
Min Minor Diameter Ext	DIE min	DIE min - (T + λ)/tan α_D