The thin head and beam provide greater access in confined areas.
 
14MM: Used on typical short-throw polishers that use a 5/16" thread such as:   
 
Griot's G9, Porter Cable etc., 
 
17MM: Used for many long throw polishers and rotary polishers
 
Check your polisher specs for correct wrench size
 
Note: Griot's Garage polishers include a wrench with their machines. These wrenches are available seperately in case of loss or damage.