O-ring sizing

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Ischgl99

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I forgot to order a -118 o-ring for my air rifle in my last McMaster-Carr order, so I tried Home Depot not expecting them to have it. They had o-rings in a package labeled #115 with the dimensions of the -118 I needed, so I bought them and confirmed the size when I got home. I have not been able to find any references to a different sizing system, is a size with # before the number instead of the dash a different system, or is this just another example of a Home Depot vendor doing their own thing? I went to Tractor Supply as well, but their 115 o-rings are the correct size according to AS568 dash system.

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If you don't have a catalog, the easiest way is to go to the McMaster Carr web site. They list all the O rings by number along with the nominal and actual sizes.
 
RJSakowski said:
If you don't have a catalog, the easiest way is to go to the McMaster Carr web site. They list all the O rings by number along with the nominal and actual sizes.
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I have already looked up the sizes at Parker, various o-ring manufacturers, as well as McMaster-Carr, I could not find any reference to a numbering system using #. The size of these is the same as -118, but is labeled as #115. My question is, is there a system that uses # and a number for the o-ring sizes as shown on the label, instead of the dash number, or is the Home Depot vendor making up their own numbering system?
 
The USA 568 -XXX numbers in McMaster Carr are those normally used throughout the industry. I have found that the numbers given by plumbing parts suppliers as typically sold by DIY stores, don't necessarily correlate the the USA 568 numbers but seem to reflect an internal numbering system.
 
I'm not aware of there being multiple systems. I am aware of Home Depot's hardware goods being eBaychina stuff in most cases. You've got to watch it carefully. More than likely that same O-ring comes labeled in two or three similar sizes and will hapily "stretch to fit" just enough times that the customer returns don't exceed the cost savings. Kind of like those red kits you can buy that end up (depending on brand and price point) that come in standard or metric sizes, but are actually the same O-ring kit, just with different stickers, "nominally" identifying the o-rings to the closest inch or metric dimension. I also suspect that these are intended mostly for faucet repairs, and may have some liberties taken to stuff cheaper materials (and probably a lower durometer materials as well) in places where stouter ones were originally called for. Barring extenuating circumstances, the Home Depot is not a place I go to for small hardware. Twenty four miles one way to them makes it kinda tough to swallow dissapointments when you get home. If you got the right actual o-ring, and it's holding air, in a fully captured and well fitting application thereby giving it some flexibility as to materials and durometer..... I'd just use it, and shake my head at what the world is coming to.
 
If you know the manufacturer of the HD O-rings, you could try their web site for their numbering system.. Danco is a manufacturer used by our local DIY.
 
If your trying to cross match, it is best to determine the nominal size of the O ring and try to match that with the candidates. If you are measuring an old O ring, remember that the actual I.D. is slightly smaller than nominal, the actual O.D. is slightly larger, and the actual width or cross section is slightly greater. To throw a monkey wrench into the mix, in addition to the USA 568 numbers, there are metric O rings as well. The McMaster Carr listing is fairly complete AFAIK.
 
Home Depot is my last choice for anything hardware related, I usually buy things like this from McMaster and build up a supply so I don’t have to look locally, but I forgot to add it to my list to buy and have the rifle apart, so I thought for a few bucks, it was worth the try. I checked some other sizes HD carries and it looks like they may be the hose sizes since the other ones I checked do not come close to the AS568 sizes, I think I might have gotten lucky that I found the size I needed. The hardware store in my town just closed down, so there is not much locally to choose from any longer.

Thanks for your assistance, it looks like this might be special numbers for Everbilt and doesn’t correspond to any list I can use if I’m in a bind again. I did find in my searching that Everbilt is owned by Grainger, but I wasn’t able to find their website to see if they have a table of sizes. Hopefully I build up a good enough selection that I don’t need to go to HD again, but if not, it looks like I’ll need to search each listing and see which one corresponds to AS568, if any others do.
 
Everbilt stuff is definitely Chinese so it's probably a metric equivalent or something
 
The size on that everbuilt package is listed as number 118 in my Hercules Seal book for hydraulic seals. So take the numbers you find at Home Depot as special all to their own.


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