M4 X .7 X 15MM 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 an 8mm (5/16″) hole
Torque Specs: 3 lb-IN