Temporarily insert a 8mm smooth rod through both LM8UU linear bearings.

Engage two M3x10 socket head screws in the hex nuts, but do not tighten them at this time.

Alternately tighten the two M3x10 clamp screws to secure the linear bearings. Slide the smooth rods back and forth while tightening.

Don't over-tighten the clamp screws; they need to be just tight enough to keep the bearings from moving.

Remove the 8mm smooth rod.