Our Moeller Adjustable Oil Filler Caps create a positive seal that cannot be bounced or jarred loose. Due to our patented closure principle, this tight seal virtually locks out dirt, dust, and other engine-killing foreign matter. This principle, developed and patented by Moeller, allows closures to seal any opening. As the handle is turned clockwise, the bottom inside the Moeller Adjustable Oil Filler Cap plate moves upward. This action causes the grooved rubber body to expand, completing a firm, positive, airtight seal. Release with a quick, simple turn of the Moeller Adjustable Oil Filler Cap handle. No special tools to worry about. Available in a variety of standard sizes. Special optional features include chains, plastic handles, and shrouded caps. We offer AC Delco and Motorcraft oil filler caps.