Remixed 1U Rack Heavy Mount Support that has a much larger surface area and is made for M5 Bolts & Cage Nuts/Standard Nuts/Wingnuts.  

Can be easily modified for M6 bolts or a wide variety of SAE bolts. Harbor Freight sells an M5/6/8 bolt/nut kit for ~6$ and I get a ton of mileage out of them for projects.

My particular use is to hold a Half-Rack Height PDU inside the rack mounted horizontally.

Incidentally this is almost obscenely strong with 6 walls & Gyroid Fill @ 20+% against X, Y & Z stress and when printed with additional overlap support blockers configured to add extra walls to the bolt barrel area and is solid as in the image.  I put a 60lb UPS and them with no real give. 

I used support blockers with a 6 layer/2.4mm wall to encase the bolt area for extra strength. Done in cura with:

-Per Model Settings -> Modify Settings for Overlaps

Printed in PLA for now but I will reprint soon in ABS/PETG when My X1C arrives for summertime server closet thermal strength.

V1.3 Moved the holes a small bit to accommodate standard M5 Cage Nuts too.  

Supports:

Doesn't Matter

Resolution:

0.28

Infill:

20% Gyroid

Filament brand:

PolyMaker

Filament material:

PLA ABS PETG CF