Being one of those guys that likes to make things myself, I got to measuring the pin thread sizes of the shackle pins and rear pivot bolts on my 1950, 3/4-ton front springs.

The 1/2 & 3/4-ton front spring, front shackle pin & bushing is a (21/32” nom.) .658”-11 thread and the 3/4-ton front spring-rear bolt is a (11/16” nom.) .683”-16 thread.
They could have just as easily used a standard 5/8”-11 pin in the front and a 3/4”-16 in the rear. It gets me to wondering if GM did it just so that you couldn’t whip those out yourself in the shop tool room of your repair shop.

Singer Manufacturing Co., makers of the Singer Sewing Machines was famous for doing that with all of their fasteners for a hundred years of production.
Denny Graham
Sandwich, IL

JOB SECURITY!

Jim.