those are standard tamiya steering knuckles. the axles should be 5mm, and are used on grasshopper, hornet, lunchbox(longer axle however), and many others.
that looks like a very cheap and easy way to get metric wheels on your jrx2.
Interesting, they were in a bag of parts I had, I am cleaning out stuff and found them. They fit snug and turn freely so whoever came up with it had an idea but it was not me.