I measured the rear pinion yoke at the point where the U-joint would sit inside of the pinion. I came up with 35⁄8 inch wide for the first measurement. I then measured the pinion at where the U-joint cup would sit or half-moon looking area. The second measurement was 13⁄16 and if I check the IEDS website I would come up with a 1350 U-joint. The 1350 U-joint is overkill for a street truck, but since I will be doing a lot of performance driving the 1350 U-joint will hold up better than a smaller U-joint.