How to choose right angle grinder gears

• Measure the outer diameter of the large driven gear (D_1) with an accuracy of 2 mm.
  
• It is not necessary to measure the outer diameter of the small drive gear.
  
• Measure the height of the large driven gear (h_1) only if necessary (i.e., if you are certain this is critical for your application).
  
• Measure the height of the small drive gear (h_2) with an accuracy of 1 mm (a washer can be used as a shim if absolutely necessary).
  
• Measure the internal diameters (d_2 and d_3) precisely using calipers.
  
• The width of the transverse slot (if present) on the small drive gear must match the width of the flats on your armature shaft.
  
• Since the reduction gear set is sold as a matched pair, it is not necessary to count the number of teeth on the gears.

Here you can select grinder gears by parameters