1-5/8 in. RED FILL CAP WITH ALUMINUM WELD BUNG1-5/8 in. RED FILL CAP WITH ALUMINUM WELD BUNGCap and Weld-On Bung InstalledProudly Made In The USA
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1 $44.99



1-1/4-12 Straight Thread
1-5/8 in. Outside Diameter Bung
1/2 in. Bung Height

Made in the USA

(Cap Replacement O-Ring is C73-749)

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 aluminum bung. 

The step ahead.

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 is supplied standard with a Buna O-ring; positive sealing and "radially squeezed " to hold the cap secure. Check out the entire line up, Billet Aluminum Fill Caps is a Pro-werks specialty.

Great 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, silver, or beautifully Micro-polished aluminum.

The right size 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.

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 !

Proudly made here in the USA.

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

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.



How do I weld my bung properly?


It is a good practice to apply several small, equally spaced tacks to minimize the potential for distortion. The bung should also be preheated and the weld should be kept small to reduce natural weld shrinkage.



The cap won't fit after welding my bung. How do I fix this?


Minor distortion of the bung from improper welding can often be addressed by applying a small amount of fine grit lapping compound to the cap threads and turning the cap back and forth in the bung to resize the threads. Do not force the process, be patient and thoroughly clean both sets of threads after the desired fit is achieved.


1-5/8 in. Red Fill Cap: C73-741
Inside Grip Diameter: 1.625 in.
Outside Grip Diameter: 1.970 in.
Height: 0.5 in.
Height: 0.312 in.
Thread: 1-1/4-12
Aluminum Weld-In Bungs: C73-747
Outised Diameter: 1.625 in.
Thread: 1-1/4-12
Height: 0.5 in.
Diameter: 1.5 in.