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Made in the USA

Pro-werks Easy Turn Filler Cap with Aluminum Weld Bung

Sale price $54.99 USD
Part # C73-739
Select Fill Cap Size First
Then Select Bung Height
Select Fill Cap Color Last
Four knurled aluminum fuel fill caps shown side by side in silver, black, red and blue finishes

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Filler Cap Specifications

1-5/8 Inch Fill Cap with Aluminum Bung

1-1/4-12 Straight Thread
Cap Weight: 1.06 oz.
1-1/2 in. Outside Diameter Bung
Bung Height is available in 1/2 in., 1 in., or 2 in. 
(Cap Replacement O-Ring is C73-749)

2 Inch Fill Cap with Aluminum Bung

1-1/2-12 Straight Thread
Cap Weight: 1.62 oz.
2 in. Outside Diameter Bung
Bung Height is available in 1/2 in., 1 in., or 2 in.
(Cap Replacement O-Ring is C73-769)

2-3/4 Inch Fill Cap with Aluminum Bung

2-1/4-10 Straight Thread
Cap Weight: 3.32 oz.
2-3/4 in. Outside Diameter Bung
5/8 in. Bung Height
(Cap Replacement O-Ring is C73-788-A)

4-1/4 Inch Fill Cap with Aluminum Bung

3-3/4-8 Straight Thread
Cap Weight: 7.86 oz.
4-3/8 in. Outside Diameter Bung
7/8 in. Bung Height
(Cap Replacement O-Ring is C74-788-A)


Easy Turn Fill Cap Advantages

The lightweight, non-vented cap features positive grip finger notches that are easy to get a hold of. Prime 6061-T6 billet aluminum is precision CNC machined into a lightweight, attractively designed cap; featuring quick-start coarse threads. Each screw on Cap is fitted with a Buna O-ring; positive sealing and "radially squeezed" to hold the cap secure. Backed by The Chassis Shop's Satisfaction Guarantee.

Perfect for Custom Tank Fabrication

Close-up of a red anodized fuel fill cap threaded onto the welded neck of an aluminum tank, with threaded fittings alongside

Installation shot of black anodized filler caps and two small breather filters with red elements on tanks in a tubular chassis, with braided hoses

Watch Product Videos ⏵

 

Get a Step Ahead

Your fabricator will appreciate the stepped shoulder at the base of the bung, it serves as a positioning locator. This feature holds the bung in place while welding in a hole of a flat surface, or in the end of tubing when constructing a filler neck extension. This grouping of cap assemblies includes a weld-able bung. 

Note:
Welding should always be performed by a qualified welder.

Close up of the stepped shoulder at the base of a Pro-Werks weld-in fill cap bung


Great Fill Caps - Great Colors

To compliment the color coordination of your project, the caps are finished off in Pro-werks Brilliance anodized colors in your choice of Black, Red, Blue, or beautifully Micro-Polished aluminum – the Pro-werks Jewelry Quality finishes are unmatched and impeccable!

Four machined aluminum fuel cell caps with scalloped grip edges, shown in polished silver, black, red and blue finishes


The Right Size Filler Cap Matters

Easy Turn Fill Caps come in many sizes and are packaged as complete assemblies with your choice of one of the many versatile mounting options, or each component is also available separately.

Set of four black anodized fuel fill caps with scalloped grip edges, shown in graduated sizes on a white background

Proudly Made in the USA

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.

You can always count on Pro-werks to do it right!



Red anodized cap with lobed grip flange, black O-ring seal and "Made in the USA" engraving, held in a hand for scale

 

Customer Comments:

"I use your bolt on caps and bungs on my carbon fiber Cummins common rail valve covers. Love the quality. Thank you."
– Randy Davis, Owner of OldSkoolFab, Inc.


"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

 

Marketing banner showing a stack of Pro-Werks fill cap brochures with blue, red, silver and black finger-notch caps, beside text inviting readers to view it

 

Complete Your Tank Build

  • Weld Plumbing Bungs — AN & NPT thread weld bungs in aluminum, steel & stainless for fuel and dry sump plumbing
  • Bar, Bottle & Universal Mounts — tank and bottle mounting solutions for your chassis build
  • Access Door Kits — aeronautical-style aluminum access doors for quick access to tanks and fill points behind body panels
Questions and Answers
How much do I need to tighten my fill cap?

It is not necessary to bottom the fill cap into the bung−just adequately seat the O-ring. The radial squeeze action on the O-ring creates a positive seal and helps prevent the cap from coming loose.

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

Applied periodically, a light coating of Dielectric grease has proven to work well as an O-ring lubricant.

Is Buna rubber compatible with my fluid?

Buna is a synthetic rubber compound suitable for use with many fluids. Buna components may need to be replaced by a material compatible with the specific chemistry of some fluids.

How do I properly weld my bung?

Apply several small, equally spaced tacks and preheat before welding. Keep the weld small to minimize potential distortion or shrinkage.

If my threads are tight after welding, how do I fix it?

The solution is simple. Apply a small amount of fine grit lapping compound to the threads then turn the cap back and forth in the bung until the desired fit is achieved. Be patient-do not force the process. Thoroughly clean both sets of threads and apply lubricant before use.

Product Videos

Two anodized fuel fill caps, one red and one blue, held in a hand, top view showing scalloped grip edges and a printed logo Video still of a presenter behind a table displaying aluminum and plastic fuel cells with a row of colored filler caps Blue anodized aluminum fuel fill cap with lobed grip, installed on a welded sheet aluminum tank sitting on a fixture table Round aluminum filler cap shown as a weld in bung welded into a flat aluminum plate, held in gloved hands, with TIG weld beads visible Aluminum canister and green-topped grip tool on a drilled fixture plate, beside a blue anodized cap marked Made in the USA, a flat file and pliers
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