4-1/4 in. BLACK FILL CAP WITH SILVER ALUMINUM 12 HOLE FUEL CELL BUNG4-1/4 in. BLACK FILL CAP WITH SILVER ALUMINUM 12 HOLE FUEL CELL BUNGShown with optional Lanyard Chain Kit installed.Provides extra large opening for fast filling.Installed on an Aluminum Tank.Installed on a Black Fuel Cell Shown with optional Lanyard Chain Kit installed.
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1 $125.99



3-3/4-8 Straight Thread
12 on 5.343 in. Dia. Bolt Circle
7/8 in. Bung Height

Includes mounting hardware and Buna gasket

Made in the USA

(Cap Replacement O-Ring is C74-788-A)

This is the "BIG ONE", the large 12 bolt circle allows for the use of the extra large 4-1/4 in. cap. When the cap is removed, the opening measures a generous 3-5/8 in. for fast filling.


Pro-Werks provides another new improvement for racers and rodders; fuel cell users can now easily upgrade from the original manufacturer provided, 6 or 12 bolt flanged, less than desirable, troublesome flip-latch style filler or bail cap - to the popular easy turn Fill Cap Assembly from Pro-Werks.

Say good-bye to pry bars.


This assembly is a simple bolt-on installation as a replacement, or right at home in new custom tank fabrication, and includes the necessary stainless mounting hardware with the Buna flange gasket.

The positive grip finger notches of the non-vented Easy Turn Caps are easy to get a hold of, this design is another Pro-Werks innovation, appreciated by everyone who uses them. The cap also has quick acting coarse threads with a starter nose to accurately lead the cap into position - a very nice feature when you are taking care of business in the dark. Each is standard with a special positive sealing "radial squeeze" Buna O-ring, which also holds the cap secure.

Great caps. Great colors.

Easy Turn caps are available in a large selection of Pro-Werks Brilliance Anodize Finish colors or beautiful Micro-polished aluminum. The bung of this assembly is also available in your choice of two anodized colors, Silver or Brilliance Black. The extensive selection of color combinations gives you the opportunity to match your individual style.

Keep your cap close.


The signature Pro-Werks Fuel Cell cap also includes a built-in lanyard boss, enabling the use of the optional lanyard chain to conveniently keep the cap close by - if you so desire.

Both the cap and bung are precision CNC machined light weight billet aluminum, right here in the USA.

Be sure to check out the entire line up - Billet aluminum Easy Turn Fill Caps are a Pro-werks specialty.   Watch the Video below to learn more !

You can always count on Pro-Werks to do it right.

Customer Comments:

"I upgraded my fuel cell to an Easy Turn fill cap assembly. It wasn't long until all my friends did the same. Great product!"
             As shared with us at the
PRI Show

Finish Your Tank

We also offer a full line of weld-in plumbing bungs to complete your tank project.

Click the images below to view all the options.



How much do I need to tighten a fill cap?


It is not necessary to bottom the fill cap into the receiving bung. Adequately seating the O-ring to make a seal is all that is required. The radial squeeze action on the O-ring creates a strong seal and helps to keep the cap from coming loose.



What should I use to lubricate a Buna O-ring?


A light coating of Dielectric grease works very well as O-ring lubricant.



What is Buna and is it compatible with my fluid?


Buna is a universal composition synthetic rubber, a standard of plumbing related products because it is compatible with many fluids. Due to the complex chemistry of modern day performance oils and fuels, you may find it necessary to replace Buna components with a material that is compatible with the unique chemistry of your specific fluids.


4-1/4 in. Fill Cap: C74-780-LB
Inside Grip Diameter: 4.25 in.
Outside Grip Diameter: 4.75 in.
Thickness: 0.35 in.
Thickness: 0.89 in.
Thread: 3-3/4-18 Thread
Aluminum Fuel Cell Bung: C74-722
Diameter: 4.187 in.
Thickness: 0.25 in.
Thread: 3-3/4-8
Thickness : 0.625 in.
Holes: 0.265 in.
Dia. Hole
Outside Diameter: 6.125 in