This Loc-Sure is a non-vented, screw-in, locking billet cap for the diesel filler neck on the 2008-2017 Ford diesel trucks (F-250, F-350, F-450, F-550). The Loc-Sure offers protection from fuel thieves and from malicious people who would contaminate your fuel. The Loc-Sure utilizes the parent company's Secure Screw system which has been tested and approved by military and other secure facilities as a low-level human secure system. The Loc-Sure features a 2.5" diameter top face with scallops and knurling for good gripping. The U-Cup seal contacts both the inside and the outside diameter of the fuel filler rim to ensure a proper seal. Each Loc-Sure purchase comes with the Loc-Sure cap and a fully machined stainless steel Pocket Secure Key with complimentary stainless steel key ring. Additional keys can be purchased using the information from our Keys page. BEM Auto's Loc-Sure body is fully machined from aluminum bars at the BEM Auto factory and is finished in a generic green anodized surface, etched to identify the assembled unit as a diesel only cap. The Secure Screw is manufactured from 18-8 stainless steel to provide good corrosion resistance.