M5 X .8 X 20MM Rubber Well Nut BY DRESS UP BOLTS

Well nuts give you the freedom and protection to secure pieces in hard to reach places that prevent you from using a normal nut. You just have to place the well nut through the opening and screw your M4 bolt-in causing it to compress and tighten.
 
IMPORTANT:
Well Nut requires a 9.5mm (3/8″) hole
Torque Specs: 5 lb-IN
Grip Range: 7.92mm (Min) – 11.43mm (Max)