14.5 versus 20 refers to pressure angle:

https://www.quora.com/What-if-we-increase-the-pressure-angle-in-gear

14.5 used to be very common. Current practice for most gearing is 20 degree pressure angle.

Zero refers to helix angle:

https://en.wikipedia.org/wiki/Helix_angle

Zero helix angle means a straight cut or spur gear.


Last edited by strokersix; 02/28/18 08:29 AM.