Tuning Brocock Bantam Sniper HR Fill Port Dowty Seal Size

This is driving me to piss! I’ve been searching for this part and size for some time and I’m tired and frustrated. I haven’t found it. Does anyone know the size needed or where I can obtain this information? I need the metal ring part within the red bracket with the worn piece of rubber around the inside of it. I’m told that this is a dowty seal, but I don’t know the size I need. 
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... a dowty seal, but I don’t know the size I need.

Do you own a caliper?

If so, measure the OD then measure the ID or measure the OD of the threads as a substitute for ID.

The O-ring material is maybe rubber.

Try to figure out what is the fitting seal material. Will a magnet stick to it? Is it soft and light like aluminum or hard and heavy like steel/stainless?

One source.

https://www.jegs.com/p/Earls/Earls-Dowty-Seals/1712764/10002/-1
 
@doubloon I do have calipers. Someone also shared a source where I can buy them, I just need to know the correct size and material. Considering that it helps seal the reservoir I want something made to handle high pressure air. I may have to resort to measuring it myself. I didn’t find any info in the manual other than a numbered diagram with no corresponding parts list. 
 
@doubloon I do have calipers. Someone also shared a source where I can buy them, I just need to know the correct size and material. Considering that it helps seal the reservoir I want something made to handle high pressure air. I may have to resort to measuring it myself. I didn’t find any info in the manual other than a numbered diagram with no corresponding parts list.

The bagnall and kirkwood site linked earlier will probably answer all your questions about size/dimension and then you'd be able to buy one that matches the dimensions from a company in MURICAH !

I found that same site earlier as well but didn't link it because you were stuck on trying to figure out the size and calipers should solve that problem which should be easy since you already have one that can be measured.
 
Ezana4CE - "I need the metal ring part". I am a little confused. It is my understanding that these are "bonded" rubber/metal washers. Perhaps I have missed something?

@shoot44 No I don’t think you missed anything. I was told by other members that the proper name for the bonded washer you’re referring to is a “dowty seal.” Let me check out your links. 

Whoa! Where did you find this parts list? I’ve been looking from one for the Batam Sniper HR. Here’s the digital owners manual https://brocock.co.uk/wp-content/uploads/2019/03/BROCOCK-HANDBOOK-2019.pdf It doesn’t contain a parts list that I’ve seen.

Neither did the the paper owner’s manual. They only include exploded diagrams. 
 

I just matched it up with some seals I already had for foster fittings, same seals as what came with my spare 1/8" bspp foster fittings. I replaced both on my Bantam .25.
 
Ezana4CE - I didn't find it, I wrote it. Like I said in my post I gathered the info from various places and just put it all together. I posted it on this forum quite a while back hoping it would be helpful.

AGAIN - IT MAY OR MAY NOT BE ACCURATE - JUST USE IT AS A REFERENCE.

@shoot44 Good effort. The company obviously protects this information concerning the build of their guns. It makes sense considering that many products are reverse engineered abroad and manufactured abroad, then sold. Brocock owners are encouraged and instructed to send their air guns to a service center for repairs for a reason. This also seems to create a dependence upon the manufacturer and their dealer network.