T-18
2. The pitch circle diameters (or pitch diameters).
3. Size of teeth (or module).
4. Number of teeth.
5. Pressure angle of the contacting involutes.
Details of these items along with their interdependence and definitions are covered in subsequent
paragraphs.
Fig. 2-1 Basic Gear Geometry
Generally:
Larger
Radius
letters
Smaller
or Radius Symbols – lower
case letters
PINION
GEAR
rbr
ra
Pitch Circle
Tooth Profile
Pitch Circle
Whole Depth (h)
Addendum
(ha)
Center
Distance
(a)
Root
(Tooth)
Fillet
Top
Land
Pitch Point
Rb
R
Ra
Circular Pitch (p)
Chordal Tooth
Thickness
Circular Tooth
Thickness
Base Diameter (Db)
Clearance
Working
Depth (hw)
Line-of-
Centers
Dedendum (hf)
Pressure
angle (a)
Line-of-Action
Base Circle
