Right this is the best I can do
I have two different brands of ball joint, One is made by Veco & the other is made by QH.
Both have the same thread.
I have just put my digital caliper on them. In metric the diameter of the treaded part is 11.9mm
Now here is the problem
Both the 20 TPI & 1.25 thread gauges fit the thread.
My Osborne cutting tool guide lists the following Two possible sizes.
M12 X 1.25 is a standard metric fine thread
7/16" X 20 TPI this is listed as a UNF thread size
Looking at my metric conversion chart, it is noted that the mertic range for 7/16" is 11.112 - 11.5mm
So given the outside diameter of the thread, it is probable that the thread is M12 X 1.25 ( Metric fine )
But I would not still rule out the 7/16" UNF in view of the possibility that this component could pre-date the metric era.
Please remember, This information taken from my tool guide & intended as a guide only
With a little luck, some of the more able engineers on the forum will have an exact answer.
