a Addendum ac Chordal Addendum anc Normal Chordal Addendum B Backlash b Dedendum C Center Distance c Clearance D Reference Standard Pitch Diameter Db Base Diameter Dc  Datum Circle Di Internal Diameter DR Root Diameter Dt Throat Diameter DO Out side diameter dp Operating Pitch Diameter F Face Width Fe Effective or Active Face Width Ft Total Face Width hk Working Depth ht Whole Depth (tooth depth) L Lead  m Module mc Contact Ratio mF Face Contact Ratio mG Gear Ratio mn Normal Module mo Modified Contact Ratio mp Transverse Contact Ratio mt Total Contact Ratio N Number of teeth or threads Ne Equivalent Number of teeth Pd Diametral Pitch (transverse) Pnd Normal Diametral Pitch P Circular Pitch Pb Base Pitch Pm True Position Pitch Pn Normal Circular Pitch PN Normal Base Pitch  Pt Transverse Circular Pitch Px Axial Pitch PX Axial Base Pitch Q Quality Number Qa Ard of Approach Qr Arc of Recess

Ot Arc of Action Rr Test Radius rf Fillet Radius, (when constant) rt Throat-form Radius rr Tip or Edge Radius of Tool t Circular Tooth Thickness tb Base Circular Thickness tc Chordal Thickness tn Normal Circular Thickness tnc Normal Chordal Thickness tr Tooth Thickness Tolerance tt Transverse Circular Thickness tx Axial Thickness Vap Total Accumulated Pitch Variation Vapk Total Accumulated Pitch Variation within a sector of k pitches Vcq Total Composite Variation (double flank) VcqT Total Composite Tolerance (double flank) Vp Pitch Variation VpA Allowable Pitch Variation Vpn Normal Pitch Variation Vq Tooth-to-Tooth Composite Variation (double flank) VqT Tooth-to-Tooth Composite Tolerance (double flank) Vr Radial Runout VrT  Radial Runout Tolerance Vs Spacing Variation Vx Index Variation VΦ Profile Variation VΦT Profile Tolerance VΨ Tooth Alignment Variation VΨT Tooth Alignment Tolerance Z Length of Action α Addendum Angle Г Pitch Angle ГR Root Angle Σ Shaft Angle ε Involute Roll Angle θ Involute Polar Angle ΘN Angular Pitch λ Lead Angle

λb Base Lead Angle λo Outside Lead Angle λp Pitch Lead Angle p Profile Radius of Curvature Φ Pressure Angle Φn Normal Pressure Angle Φt Transverse Pressure Angle Φx Axial Pressure Angle Ψ Helix Angle, Spiral Angle Ψb Base Helix Angle A Allowable Variation G Features on a gear K A Variable n Normal Plane P Features on a pinion T Tolerance t Transverse Plane W Features on a Worm