In FOX fashion, they made many variations of similar parts. This one has a 6-40 thread and a 1/16" diameter needle that extends out of the knob around .580". We found it is used on the large flange mount carburetor and the small square necked carburetor used on the 36 & 40 engine with the six screw back cover.

We found another needle with an 8-60 thread so you may want to check yours. Measure the outside diameter of the thread on the carburetor.
A 6-40 thread measures about .135" dia and an 8-60 is about .165" dia..

We also suggest checking your thread pitch.
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