14.5 versus 20 refers to pressure angle:
https://www.quora.com/What-if-we-increase-the-pressure-angle-in-gear14.5 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_angleZero helix angle means a straight cut or spur gear.