I was having some issues with the Y-Axis coupler freeing itself while in use, making the laser cutter unreliable when moving at higher speeds on the Y-Axis
I had a look online, and no where seemed to sell steel rigid thick long couplers for 5 mm shafts.
So I had a friend who has a lathe make one for me out of steel.
Here is the product he made for me
Here is my original coupler - made of aluminium with 3mm grub screws. (As you can see I already lost one of the grub screws, so used a normal 3mm screw in it's place.
Its not the size, its what you do with it.. is what every girl tries to tell you when they just want to make you feel better...
Slides on perfectly to the 5mm rod
Here it is fully installed.. working perfectly.