This is very important, try to think of it like this, YOU ARE NOT TIGHTENING ANYTHING... You're assembling it. Same goes with all fasteners(learn about fastener torque). Once the slider is threaded onto the Slider Core to the bearing STOP! Just touch it and THATS ALL!
THE MOST IMPORTANT PARTS OF THIS ASSEMBLY IS TO NOT CROSS THREAD THE SLIDER ON THE SLIDER CORE! AND DO NOT TIGHTEN IT, JUST "SNUG" WITH NO END PLAY!!!
Press the two bearings into the Slider Housing, press the Slider Core(it should be a light press fit, do not remove any material to make it fit) through the Slider Housing and thread the Slider onto the Slider Core. PAY ATTENTION TO WHAT YOUR DOING!
Remember the small precision drill chuck... USE IT HERE!
You DO NOT want to GRAB this part WITH the nasty jaws of some funky PLIERS... (Honestly I can never figure out why people have pliers except needle nose, most are made for working with wire and fencing etc...) not work holding or nut & bolts.
Almost Done...