I have been playing with some 3d printed antenna components and needed/wanted a hardware component for reliable, repeated, connections of components with a 3/8 - 24 thread pattern.  Most hardware options I found were pretty pricey for what you get & shipping made it worse.  

I ran across the following on Amazon w/free shipping if Prime.  They are listed as axle extensions for training wheels on Huffy bicycles & have the 3/8 - 24 threads, male & female.  $6.99 for two.

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They are working well for what I've been doing.

Nice, I could have used that for the top of my 3D printed adjustable loading coil.  I went with long bolts and coupling nuts to make the "female" side connections.

Good find!  I added these to my shopping list in case I need them for a project later.