Summary

CR-10 (at least my V3 version) bed is 320mm in Y axis but is limited by the endstop to 310mm. This mod moves the endstop little further and adds those sweet additional millimeters. It's not much but when you need to print 315mm long thing, it's a real lifesaver. It's adjustable but I personally have it flush with the 2020 extrusion.

It could probably go to 330mm but it would require 330x310mm bed plate which are not available.