If you are measuring for proper u-joint size of your existing pinion yoke or measuring to purchase a new pinion yoke.
#1 How wise is the saddle that the u-joint cap fits into?
You will get ONE of theses three choices 1-1/16 , 1 -1/8 , 1- 3/16
#2 What is the measurement Between the 2 locating tabs?
3-7/32 or 3-5/8