That notch on my version was used to add the Z-endstop adjustable bolt. While I am at this, I should upgrade this to something newer. What type of adjustable Z-endstop are most people using now? I see at least a couple of different ones on thingiverse. Here are the ones that I found. http://www.thingiverse.com/thing:545105 and this one, http://www.thingiverse.com/thing:321810 I have added the extra welds & will take out that little bolt hole & notch.IMG_7863_800x600.jpg