Fuel Cell Filler 12 Bolt Flange Material: 6061-T6 Aluminum Alloy. Fuel Cell Filler 12 Bolt Flange Base: Rubber. Fuel Cell Filler 12 Bolt Flange OD: 5.5" (140mm). anodized finish. The Straight Fuel Cell Fast Filler Neck are Designed for those who need to fuel their vehicles as.