The hole for the nut inside the red circle in pictures #2 and #3 is round, it is not a hexagonal nut trap as those other two holes are. The nut will be spinning in place when tightening it. Shouldn’t a screw head go in there instead and use a nylon nut on the bed’s side? Or fix the STL file and make the hole hexagonal. It was round on both MK2.5/MK3 cover I printed/got recently.
The manual for MK2S (step 15 Y-axis) recommends this: “On side with two bearings slide bearings to the center, towards each other as close as possible”. Why for the MK3 it’s recommended to center the bearings in the hole instead of pushing them to the side? Shouldn’t the instructions be the same?