1/4-28 is the actual size of the threads, 1/4" diameter...but 1/8" pipe
is bigger, actually about 3/8" diameter threads...and it's a tapered
pipe thread. Not sure about AD trucks, but TF trucks use plenty of
each. For example shackle zerks are 1/4, while kingpin zerks are 1/8
pipe (if memory serves). You really have to take a look at all of
them. Also, you may find some that have a 1/8" pipe thread into the
part, and an adapter, usually at an angle, with a 1/4-28 zerk fitting
screwed into it.
Jim
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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