Sk8Kings - Sex Bolt / T-Nut Mounting Hardware (One Set = 4 nuts/4 bolts) 
Extra durable steel sex bolt / t-nuts - This  hard to find old school style hardware item is perfect for mounting skid/grind plates.  Mounts flush and sturdy with included phillips head bolts and cylinder sleeve nuts. 
Sold in a set of 4 bolts with nuts (8 pieces total).  Hardware finish may vary from photo (all black currently) subject to available stock.  
Deck Rail Mounting:  You may need to alter the pre-drilled holes on recently manufactured rails (ie Powell and Pig rails) in order to use this sex bolt mounting hardware for that purpose. 
Mounting Notes: Drill deck to insert  cylinder nut  from top  (so the low profile head is nearly flush with the deck top) and insert bolt up through the bottom - tightening into the cylinder sleeve nut - similar to the way a typical lock nut would work. Use drill bit size 7/32.