Pro-werks Easy Turn Filler Cap with Aluminum Bolt-On Bung
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Bolt-On Filler Cap Specifications
1-5/8 Inch Fill Cap with Bolt-On Bung
1-1/4-12 Straight Thread
Cap Weight: 1.06 oz.
4 on 2 in. Dia. Bolt Circle
9/16 in. Bung Height
(Cap Replacement O-Ring is C73-749 & Bung Replacement O-Ring is C73-748)
2 Inch Fill Cap with Bolt-On Bung
1-1/2-12 Straight Thread
Cap Weight: 1.62 oz.
4 on 2.25 in. Dia. Bolt Circle
9/16 in. Bung Height
(Cap Replacement O-Ring is C73-769 & Bung Replacement O-Ring is C73-768)
2-3/4 Inch Fill Cap with Bolt-On Bung
2-1/4-10 Straight Thread
Cap Weight: 3.32 oz.
5 on 3.125 in. Dia. Bolt Circle
11/16 in. Bung Height
(Cap Replacement O-Ring is C73-788-A & Bung Replacement O-Ring is C73-789)
Bolt-On Bung and Filler Cap Assembly
The Pro-werks Bolt-on filler cap assemblies require no welding; this produces a very clean finished installation every time. The base of the Silver anodized aluminum bung is machined to accept the provided Buna O-ring for a positive seal, mounting hardware is included.
There are many very useful applications; ideal for composites when welding isn't an option and thin gauge materials that are too difficult to weld, or any installation that already has a sensitive protective finish applied. These are also a favorite of engine builders for filling oil in a valve cover.
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.

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Leak-Proof O-Ring Seal

Great Filler 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!

The Right Size Fill 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.

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!

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
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?
What should I use to lubricate the Buna O-ring?
Is Buna rubber compatible with my fluid?
Pro Tips
Formula to calculate fluid capacity of a tank
Product Videos










