# O-Ring Groove Sizes



## MrNaz (Jul 2, 2009)

Previously I was stabbing in the dark when deciding on groove sizes for orings, and then I found a technical document from an engineering company. It was all in imperial units, so I converted it to metric, selecting the orings that flashlight modders and builders are likely to use. Here are the values, I hope someone finds this useful!

*CS GD GW*
1.60 1.17 2.21
1.78 1.25 2.54
2.00 1.44 2.81
2.50 1.89 3.37
2.62 1.98 3.48
3.00 2.23 3.99
3.53 2.74 4.52
4.00 3.18 5.12

CS = Cross sectional diameter of oring
GD = Suggested Groove Depth
GW = Suggested Groove Width

These values result in optimal compression of orings, and the information was found on this page:
http://www.row-inc.com/sizes.html

Is there a place I can add all the useful technical data I am collecting? It seems that this is the sort of information that people must look up again and again, and it'd be useful if there was some central repository for this knowledge. Or is the collective CPF mind supposed to do that? :twothumbs


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## darkzero (Jul 2, 2009)

Good info. I think I seen this before but not sure if it was here. Would be good to add it here:

common dimensions reference thread 

or here:

Common Machining Info 

Both these threads can be found in the sticky in Materials/Mechanical/Machining:

threads of interest


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## Th232 (Jul 2, 2009)

I've just been going through this problem myself, great find, thanks!:twothumbs


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## Packhorse (Jul 2, 2009)

Are you sure those figures are correct?
I would have thought the GD and GW for a 4mm O ring would be twice that of a 2mm O ring.


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## MrNaz (Jul 3, 2009)

Packhorse said:


> Are you sure those figures are correct?
> I would have thought the GD and GW for a 4mm O ring would be twice that of a 2mm O ring.



Yea I made a mistake in the metric conversion, edited and fixed. However, it is not true that double oring CS means double GW and GD, as optimum compression ratios vary in a non-linear manner to oring cross sectional area due to the differing proportional force required to compress orings of different size.


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## dom (Jul 4, 2009)

Here's a very handy chart
The website that hosted it is gone,so i had to
scan the pages i had. 

It was originally 2 pages long -so you may have to download the file 
and print it to see it properly.








If you go to this link -you can click "All Sizes" and select the size you want to download.
http://www.flickr.com/photos/[email protected]/3686395415/



Cheers
Dom


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## BoarHunter (Jul 5, 2009)

MrNaz said:


> Yea I made a mistake in the metric conversion, edited and fixed. However, it is not true that double oring CS means double GW and GD, as optimum compression ratios vary in a non-linear manner to oring cross sectional area due to the differing proportional force required to compress orings of different size.



There is no need to convert but to use standard metric sized O ring.
Even US suppliers have metric O ring in their catalog while outside of the US it is far less common to have inch (nobody makes new design in inch even in the UK !) and in fact not advisable to deviate from standard ISO.

There are cutting tools that provides you the exact groove needed. Do some reading too to determine the grooves based on how the O ring is used. Note for a flashlight it is quite simple too.

Note that a good place to get O rings in limited quantities are plumbing and automotive stores. They have many sizes suitable.
A very common cross section is 1.8mm.


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