Added a V2, just slightly bigger holes for the bolt and allen key making them easier to fit
Purpose:
Liked the original, but like requested in the comments for it, I also wanted M5 fitments
Removed internal filleting and recess
Removed bolt bump so and not needed with M5x8mm bolts
Included a 105mm (alongside the 125mm) for the sides of the Ender 5 Plus that are 2040
Notes:
Tried modifying the STL in Fusion360 and didn't get anywhere so completely redrew the model, only interested in the 125mm version at the moment - included the STEP modify if you want
Bolt will need to be slipped in from the side - opening through the outside is 3.5mm so JUST ABOUT big enough for an allen key
If you are adding without disassembly its tricky - but not impossible... method below!
I screwed in bolt fully then retracted so the thread was cut, added the t-nut to the vertical side of the frame and turned with a little screw driver which I also used to hold in place then placed the support over the top of the t-nut. It's easy to tell when its in the right place as the support seats against the frame. I secured the M5 by a few turns and then added the horizontal t-nut, also turning to secure orientation and then just slid the support to it