3Drag: improved y-axis linear bearing holder

🇪🇺 I've decided to move my 3D models to a different website. The files for this Thing can be downloaded here: https://www.printables.com/model/1233330 🇪🇺

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I've had some problems with ripples in my prints or even missed steps. After some investigation and experimentation I found out that the reason seems to be the sturdiness of the y-axis linear bearing holders - or rather the lack of such. Because the holders are just held by one screw each, they can be slightly tilted, not holding the be