Here's how I make trike trackrods:
I'm using M8 trackrod ends - a type of ball-joint.
Other materials I am using are some M8 machine screws with the head cut off, and some scrap fibreglass and aluminium alloy tent poles.
First I use an 8mm tap to cut a thread in the alloy tent pole. A 35mm length is cut off, the tube faced in the lathe and the end tapped again until I have 4 made. The tube is only about 9mm, so the tap actually stretches the tube a bit too. I'm using the tap dry as I do not want grease around.
The GRP tubes are cut to length...
...and the ends turned down to fit in the alloy tube. I am starting from the shoulder end, so that the fibres get cut through.
These threaded ferrules are part filled with epoxy (with the threaded studs just started)...
...the studs are threaded a bit further in and then the GRP poles inserted. When the epoxy starts to set, they are cross drilled 1.5mm, and panel pins riveted through both the stud and the GRP to the alloy ferrule.
The new rod compared to the too-short ones removed from an old project trike.
(I had used wider, thicker aluminium tube when I made the first ones)