Pitch nomenclature Gear

pitch distance between point on 1 tooth , corresponding point on adjacent tooth. dimension measured along line or curve in transverse, normal, or axial directions. use of single word pitch without qualification may ambiguous, , reason preferable use specific designations such transverse circular pitch, normal base pitch, axial pitch.

circular pitch, p 
arc distance along specified pitch circle or pitch line between corresponding profiles of adjacent teeth.
transverse circular pitch, pt 
circular pitch in transverse plane.
normal circular pitch, pn, pe 
circular pitch in normal plane, , length of arc along normal pitch helix between helical teeth or threads.
axial pitch, px 
linear pitch in axial plane , in pitch surface. in helical gears , worms, axial pitch has same value @ diameters. in gearing of other types, axial pitch may confined pitch surface , may circular measurement. term axial pitch preferred term linear pitch. axial pitch of helical worm , circular pitch of worm gear same.
normal base pitch, pn, pbn 
an involute helical gear base pitch in normal plane. normal distance between parallel helical involute surfaces on plane of action in normal plane, or length of arc on normal base helix. constant distance in helical involute gear.
transverse base pitch, pb, pbt 
in involute gear, pitch on base circle or along line of action. corresponding sides of involute gear teeth parallel curves, , base pitch constant , fundamental distance between them along common normal in transverse plane.
diametral pitch (transverse), pd 
ratio of number of teeth standard pitch diameter in inches.





p


d



=


n
d


=


25.4
m


=


π
p




{\displaystyle p_{\rm {d}}={\frac {n}{d}}={\frac {25.4}{m}}={\frac {\pi }{p}}}


normal diametral pitch, pnd 
value of diametral pitch in normal plane of helical gear or worm.





p


n
d



=



p


d




cos
⁡
ψ





{\displaystyle p_{\rm {nd}}={\frac {p_{\rm {d}}}{\cos \psi }}}


angular pitch, θn, τ 
angle subtended circular pitch, expressed in radians.




τ
=


360
z




{\displaystyle \tau ={\frac {360}{z}}}

degrees or






2
π

z




{\displaystyle {\frac {2\pi }{z}}}

radians




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