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I've looked around online but haven't been able to find just the gasket by itself. You can get it with a new cap of course but I'd rather just get the gasket if I can.
 

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If it's an O ring you can usually find one at most hardware stores in those drawer sections of screws washers etc. trial and error to fit . . . .
 

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Assuming it's an O-ring, if you can't find one at your local hardware store, you can find sites online that sell them. You can also buy the round material, cut to length and glue the ends together with super glue to make the ring.

Note that Hunter almost certainly bought the fuel fitting from another manufacturer. Identify who and they probably can sell you a gasket.
 

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Heath2,

We use silicone o-rings for all our deck fills. They last a very long time and aren't as affected by UV if they are slightly exposed [which they shouldn't be...]

Here is the size we use for fuel and water fills....
NOT A GOOD IDEA FOR FUEL FILL. Silicone is attacked by aromatic hydrocarbons (diesel fuel and gasoline). Just check this compatibility chart or read the Amazon description you linked:

Silicone is vulnerable to mechanical wear and tear, water and steam over 250 degrees F (121 degrees C), aromatic hydrocarbons (benzene), chlorinated hydrocarbons (trichloroethylene), acids and bases, and hydrocarbon fuels.
For fuel fills, you need Viton, which is the material that all factory-supplied fill caps come with.

Additionally, the 1/8" width that you linked is about twice the width of every fill cap gasket that I've ever seen.

I am looking for a gasket for one of my water fill caps, so would appreciate learning the standard dimensional specs from someone who has measured their fill cap.
 

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Thanks, Rick,

You are absolutely right about silicone not being the best choice for seals in routine contact with liquid diesel.

Why have we not seen any degredation due to exposure to diesel fuel or diesel fumes? Probably because the primary purpose of the o-rings on our fuel fill caps [and other deck-fills] is to keep contaminants out of the tank. [liquid and solid...]

One could argue a secondary purpose is to keep fuel in. However, on our boat, unless we suffer an extended knockdown beyond ~110°, or a roll-over, liquid fuel will not contact the cap o-rings. [Fumes will, but don't seem to cause any issues over the years we have been using silicone...] Of course one could also put the cap o-ring in contact with fuel through sloppy fuel filling practices.

In our case, we were constantly fighting the cracking and checking of Nitrile, Buna-N, Vitone, etc. [Including the new o-rings stored for future use.] And so far, silicone lasts the longest for us [years in use and extended shelf life of spares] and so far has never checked or degraded to cause a leak.

Therefore, we opted years ago to use silicone o-rings on our deck-fill caps to help mitigate the small [water] leaks checked o-rings ultimately allow if left undiscovered. [We cruise in remote places so contaminated fuel is not easily dealt with nor a minor inconvenience. In fact, a future project is to install ball valves under the deck fills to further protect against any contaminant ingress- or hanky-panky... I'm waiting until I'm in a contortionist mood for that project...]

O-ring size was also mentioned: The o-rings I linked fit our standard 1.25" female NPT deck fills perfectly without any o-ring exposed after the cap is properly tightened. [We do need a larger ID o-ring for our 1.5" NPT waste pump-out caps, but these would stretch to suit if they were all we had.]

In hopes this helps describe the reasons why- at least in our use cases- silicone makes a lot of sense.

Of course everyone should use what is ideal for their individual use cases and what they are most comfortable with...

Cheers! Bill
 

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Sounds like the right trade-off for you, and potentially for many others. There is no perfect material, so there are always compromises to be made. You are right that even the fuel fill does not directly expose the O-ring, especially with the low volatility of diesel fuel. I would be more concerned about fume exposure for those who still have gas motors, but for most of us it's probably fine.

My 16-year-old boat has O-rings that are all in perfect condition, except for one of the water tanks. (I'm looking to replace that one.) Maybe the good ones are newer because they might have been replaced by a prior owner. Or maybe we're in higher latitudes where the sun is less intense and shines down at a lower angle.

It's all good advice. Mine was stated a little too bluntly.
 
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