Button Head M3x8mm. Attach the X axis to the linear rail carriages.

After attaching the X Axis, move it upwards to its top position, making sure it's level, and firmly tighten these 4 screws, making sure the plates don't twist.

Slide the X Axis up and down throughout its entire range of movement to ensure that the 2 Z Linear Rails are perfectly parallel. If the carriages bind at any point, you will need to adjust their positioning.

To do this, start by tightening the screws on one of the Linear Rails first, while leaving the other Rail loose enough that it can move. Slide the X Axis all the way through, up and down, to establish the correct position, and then tighten the second linear rail. Start by tightening the screws at the tips and work your way inwards.

This step is very important to get the best performance. Take your time to get it right.

After everything is tight, align the Anti-backlash nuts flush against the tips of the 2020 profile. While positioning the Anti-Backlash nuts, make sure the Lead screws are straight and parallel between themselves as well as the 3060 Z pillars. They should not be tilting away or towards the pillars. Tighten the screws.

If later in the build you install the Z Tops (printed parts), you can look directly down through their top hole to make sure the Lead screws are perfectly straight.