Through CAD alignment is easy for gears by sketching out the distance in which the pitch circles of two gears are tangent
For sprockets and pulleys an ideal center-to-center distance can be made between holes
In Onshape assemblies revolute mates simulate gear ratios through the ‘gear relation’ tool which simulates gearing between two revolute mates
Symbol is below
Pitch - the set distance between two teeth
Pitch diameter/pitch circle diameter - it's the imaginary diameter of where the widths of the teeth and spaces in between the teeth are equal
These are the same for sprockets and pulleys