In addition to Elco Jacob’s comment I would like to add that even if your printed parts are perfectly square and a snug fit to the 2020 extrusion and other parts, there can still be a problem with skewed plates that mount on the rail carriages. I don’t like solutions that are irriversable (such as sanding something down) without understanding what the actual cause is. So I looked closer into the problem. My parts were square and as good as you can expect from a printed part. Yet, when I tightened the bolts that hold the printed part to the extrusion, the plates skewed with their outer tips down by 0.15mm to 0.2mm left/right. What I did was test which one of the bolts could be fastened without the plate skewing. This were the top bolts. I then shimmed the space at the bottom bolts so it could no longer skew when tightened. This fix is actually closer to the real issue in my case, and is reversable and adjustable. Hope that helps!
In addition to Elco Jacob’s comment I would like to add that even if your printed parts are perfectly square and a snug fit to the 2020 extrusion and other parts, there can still be a problem with skewed plates that mount on the rail carriages. I don’t like solutions that are irriversable (such as sanding something down) without understanding what the actual cause is. So I looked closer into the problem. My parts were square and as good as you can expect from a printed part. Yet, when I tightened the bolts that hold the printed part to the extrusion, the plates skewed with their outer tips down by 0.15mm to 0.2mm left/right. What I did was test which one of the bolts could be fastened without the plate skewing. This were the top bolts. I then shimmed the space at the bottom bolts so it could no longer skew when tightened. This fix is actually closer to the real issue in my case, and is reversable and adjustable. Hope that helps!
It should be noted that the end stop is attached with M5x12 and M5 t-nut 3030.