Fuel filler O ring size

[eddystone]

I’ve always used a size 29 O ring on Sowester fuel filler cap ( no idea what that means - it’s certainly not mm) but noticed the other day that “27” is cast into the underside of the filler so I used that size although it needs more stretching . Is the 27 meant to be the 0 ring size I wonder?

 

[Plum]

I’ve always used a size 29 O ring on Sowester fuel filler cap ( no idea what that means - it’s certainly not mm) but noticed the other day that “27” is cast into the underside of the filler so I used that size although it needs more stretching . Is the 27 meant to be the 0 ring size I wonder?

Don't know for sure but maybe the French Oring standard sizes? French R Standard O-Ring Sizes

www.solocoastalsailing.co.uk

 

[Malish]

Suspect you need to ask simply bearings
Simply Bearings Ltd
I'm sure it would be helpful if you had the old o ring and the cap to hand along with a caliper gauge

 

[Daydream believer]

For how cheap they are ( less than £15) I am surprised some do not have a box of "O" rings.
Always handy if you never need them.

 

[savageseadog]

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[Daydream believer]

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If I try to overtighten my deck filler then I cannot get it undone. A ring sprung tight around the base of the threads seems to do the job perfectly adequately. One fitted in the face in a recess would just drop out which could be a pain considering the number of times it is removed.- ie My water tank is filled every 3 days when I am aboard.
I can see the benefit for such a design for a more permanent fitting though, ie the water pump speed seal cover.

 

[Refueler]

Not meaning to be rude ... but surely when it comes to O rings in such a job - then local Motor Factors usually have loads of rings of different sizes ... at cheap as chips prices ... take cap to Factors ... they measure ... bobs proverbial ....

Question though ... surely an O ring in such duty should last years ???? especially if petroleum resistant type fitted ??

 

[superheat6k]

In addition to the o ring I apply a decent volume of waterproof grease. This stops the cap seizing and seals the threads against water ingress.

For the o ring measure the recess OD and average thickness of the old o ring, then look these up in an o ring table. '29' is possibly BS 029