① Spiral angle of two gears:
β1=0.5×(Σ-1)
β2=β1
② Two gear indexing cylinder helix angle:

③ Two gear base cylinder helix angles:

④ Helical angle of two gear segments:

⑤ Pressure angle of normal pitch circle of two gears:

⑥ Pressure angle of end pitch circle of two gears:
