These are custom stainless tamper proof sheet metal screws measuring 6-18 X 1/2 inch in length.  A tamper resistant one way oval head is incorporated with type A sheet metal screw thread.  We have these parts manufactured domestically at 30,000 to 50,000 pieces and release them to our customer as needed throughout the year.  18-8 stainless steel material is used on these specific one way oval screws but we also supply an identical part in 316 stainless steel material.