12 bolt rear axles

[aggie91]

Well guys I ran into a new one for me...

I have a '73 (per the title, '74 per the VIN) Suburban that I picked up and did some investigation on the rear axle for servicing it. It turns out it is a 3.07 gear with a factory LSD carrier and the pinion yoke takes a 1330 series U-Joint. The ring gear is stamped 14 43, which works out to a 3.071428571 ratio.

I also have another 12 bolt from a square body (not 100% sure what it originally was in before I got it). It is has 3.07 gears and an open carrier. The pinion yoke on this one takes a 1310 series U-Joint. The ring gear is stamped 15 46, which works out to a 3.066666667 ratio.

All the other 12 bolts that I have and have had in the past have the same pinion yoke size that uses the 1310 u-joint.

Has anyone else seen 12 bolts with the same ratio, but different tooth counts and a different pinion yoke?

Would GM make multiple sets of gears that work out to the same ratio for the same type of axle? What would be the reason to do so?