1/4-20 x 1-1/2" Button Head Torx Security Machine Screw Bolt Screws Stainless Steel Tamper Resistant, Qty 10 Thread Size 1/4-20 x 1-1/2" Length by Fastenere: Amazon.com: Industrial & Scientific
Amazon.com: Stainless Steel Sign Mounting Hardware Tamper Proof Star Drive Screws with Security Nuts Kit 5/16"-18 x 2" for U Channel Post - 25 Pieces : Industrial & Scientific