# Best flashlight O-ring material..and more.



## donn_ (Dec 23, 2008)

I've decided to put together a supply of o-rings for flashlights, and want to compile a list of appropriate materials and sizes.

Here are the materials available:

Buna-N
PTFE
Kalrez Perfluoroelastomer (whew!)
Viton
EPDM
Fluorosilicone
Silicone
FEP-Encapsulated
Aflas
Neoprene
Polyurethane
Hytrel

Please give me opinions, including reasons why. I figure different locations on different lights will call for different materials, ie: more heat resistance on head rings in hotwires, etc..

I'd also appreciate any size lists, or links to sizes for various lights, including Surefire, Maglite, Aleph, McGizmo, Mr. Bulk, ArcMania, etc..

Thanks in advance!


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## donn_ (Dec 23, 2008)

I'll keep the list here. I'm using the industry standard "Dash #" when applicable.

Aleph tube switch end: 015
Aleph tube head end: 015-017
Aleph Mule head inner: 017
Aleph Mule head outer: 018
McLux PR, PR-T, Aleph, Longbow PR heads: 023
Aleph 2, Aleph 19 and McLux PD head: 019
Aleph 3 head: 36mm(ID)x3mm(thickness)
Lummi Raw NS/Al/T1: 16mm(ID)x1mm(thickness) 
Lummi Wee NS/Ti: 11mm(ID)x1mm(thickness)
Lummi Wee NS/Ti, switch: 6mm(ID)x1mm(thickness)


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## Yoda4561 (Dec 23, 2008)

I figure the best ones from a chemical standpoint are going to be the fluoro-whatever ones. Usually plastics that are fluorinated have near-perfect chemical resistance. I've heard that butyl(I think that's buna-n, or was that nitrile?) is best for mechanical sealing and durability among the common rubber o-rings.


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## precisionworks (Dec 23, 2008)

I often refer to this chart from Marco: http://www.marcorubber.com/material_chart.htm


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## Sgt. LED (Dec 23, 2008)

I'd love to have a set of O-rings in multiple colors for my Aleph Mule. Blue orange red yellow! Not sure where or if some of those colors are offered. The exterior window lens and the boot retaining ones are the only ones I would want to bother with. 
I have the black EN one and colors would look really nice in contrast. The Mule is with Milky right now but on it's return I am going to try to put in GITD ones I got from Sigman.


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## csshih (Dec 23, 2008)

ooh. can anyone post where to get these o-rings cheaply?


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## saabluster (Dec 23, 2008)

csshih said:


> ooh. can anyone post where to get these o-rings cheaply?


I get mine at smallparts.com.


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## Black Rose (Dec 23, 2008)

csshih said:


> ooh. can anyone post where to get these o-rings cheaply?


I get generic o-rings from dealextreme.

Thanks for that link saabluster.


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## Mirage_Man (Dec 24, 2008)

donn_ said:


> I'll keep the list here. I'm using the industry standard "Dash #" when applicable.
> 
> Aleph tube switch end: 015
> Aleph tube head end: 015-017
> ...



Donn, is this the A1 head? I was just getting ready to do a search to find out the size of that o-ring.


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## Mark A. (Dec 24, 2008)

An excellent source for O-rings and for technical information regarding them is www.applerubber.com
Apple Rubber sells to the aerospace, military, and medical industries, to name just a few.

A good source for small quantities is McMaster-Carr, which is www.mcmaster.com
McMaster also has a great search engine & filters that would help someone determine the dash number of any proposed O-ring, if available.

Mark A.


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## PEU (Dec 24, 2008)

I always used Nitrile/Buna-N orings for my builds, never a problem with oils or lubricants. I buy at a local ISO9000 manufacturer, these aren't expensive unless you go name brands such as Parker, etc.


Pablo


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## LuxLuthor (Dec 24, 2008)

precisionworks said:


> I often refer to this chart from Marco: http://www.marcorubber.com/material_chart.htm



Great resource!



saabluster said:


> I get mine at smallparts.com.



Also a very handy site.



Mark A. said:


> An excellent source for O-rings and for technical information regarding them is www.applerubber.com
> Apple Rubber sells to the aerospace, military, and medical industries, to name just a few.
> 
> A good source for small quantities is McMaster-Carr, which is www.mcmaster.com
> ...



I forgot how much I needed various O-Rings for an assortment of lights and household things. The problem with those typical assortment kits is that they have mostly the same black material, and only larger O-Rings. McMaster's costs $5-6 for a minimum quantity of each size O-Ring plus shipping.


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## Mark A. (Dec 24, 2008)

Donn,

Rob is good enough to post O-rings sizes (and kits of them for sale) on his Lummi site. Find such offerings here: http://web.mac.com/Lummii/Lummi2/Extras_Options_&_Parts.html

Mark A.


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## donn_ (Dec 25, 2008)

Thanks for all the replies.

McMaster-Carr will be my source for most, if not all of them. I receive 1-2 orders from them every week, and will just add to these orders until I have all I need. Place an order one day, and receive it the next. Great service and an astonishing inventory.

I'm particularly frustrated I can't find the dash# of the various Maglite rings. All I can find is their part#, but they are generally way overpriced. I guess I'll have to break down and measure them, and see how close I can get.

Thanks for the tip, Mark. I'll add Rob's sizes to the list.


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## donn_ (Dec 25, 2008)

Mirage_Man said:


> Donn, is this the A1 head? I was just getting ready to do a search to find out the size of that o-ring.



I haven't found the Aleph 1 head ring yet, Brian. All the rest are from the Shoppe, but if they list the A1, it's well hidden.

Edit:

On a second look, the 023 ring listed for all the PR heads and Aleph, may well be for the Aleph 1. 023 is 1.051" x 1.191" (ID/OD). That's dangerously close to 27mm.


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## csshih (Dec 25, 2008)

thanks for the site, saabluster.


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## mosport (Dec 25, 2008)

Here's another good online resource when evaluating material suitability, I've had good luck custom sizing automotive seals from this local manufacturer-dealer in the past.

Elastomer Temperature Range chart

General Physical Properties


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## Boltgun (Dec 26, 2008)

The Viton O-rings will be good for heat. One of the smaller ones is used in the AR-15 bolt to assist in extraction. This is subjected to noticable heat during long firing sequences. I would have no reservations about using that brand. 

Boltgun


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## precisionworks (Dec 28, 2008)

Another great resource, this one from Parker Hannifin Corporation • O-Ring Division:

http://www.sealingdevices.com/orings/oring_chemicalcompatibility.pdf

At 53 pages total, there's a ton of info.


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## underwatermike (Jan 19, 2009)

Use nitrile (buna-n) or viton. Either will work. The important thing is to get the proper interference fit. A minimum interference fit of .010 and a maximum fit of 0.28 is the range to work in. The Parker seal catalog is the standard reference on this.

The 70 durometer O-rings should work just fine. 90 durometer will work also, but will be harder to assemble.

Unless you have a special application, any source of O-rings should work. I buy from McMaster unless I need traceability. Then I go to a local seal specialist.

I used to run an elastomer testing lab. O-rings are easy once you learn how to design a proper seal glang.

underwatermike


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## Mirage_Man (May 5, 2009)

Anyone know the correct number for the 38mm Aleph window? I found a post that said it's a #31 but that seems a little big to me.


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## donn_ (May 5, 2009)

I use a metric size, 36mm x 3mm, in Buna-N. McMaster-Carr item # is 9262K295.


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## Mirage_Man (May 5, 2009)

donn_ said:


> I use a metric size, 36mm x 3mm, in Buna-N. McMaster-Carr item # is 9262K295.



Yeah, I saw that you did for Erin's 38mm head. I was just wanting to know what the spec'd one is for the original A3.


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## choffman (May 5, 2009)

Boltgun said:


> The Viton O-rings will be good for heat. One of the smaller ones is used in the AR-15 bolt to assist in extraction. This is subjected to noticable heat during long firing sequences. I would have no reservations about using that brand.
> 
> Boltgun




+1 Viton rings are also used in sprayers that contain solvents used for auto paints. VERY good chemical resistance. Ironically, hf sells a set of them item # 95450. I don't know about the quality from hf, I've just seen the assortment set in the store.


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## RocketTomato (May 5, 2009)

Viton is a great material but it can be a little expensive and the extra chemical resistance is not really necessary for flashlights.

EPDM is relatively cheap and holds up better to steam, ozone and sunlight then Buna-N (A.K.A. Nitrile)

Silicone is more expensive then both EPDM and Buna-N and has a very large useful temperature range (-80 to 400 F) but it abrades and tears easily so it is not recommended for dynamic seals, i.e. like on a piston light or a twisty.

Kalrez is even better then Viton but very expensive. 


I have also compiled a large list of o-rings used in flashlights over here.


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## wykeite (May 7, 2009)

underwatermike said:


> Use nitrile (buna-n) or viton. Either will work. The important thing is to get the proper interference fit. A minimum interference fit of .010 and a maximum fit of 0.28 is the range to work in. The Parker seal catalog is the standard reference on this.
> 
> The 70 durometer O-rings should work just fine. 90 durometer will work also, but will be harder to assemble.
> 
> ...


 

Good job I read through the thread, it's more or less what I was going to say without mentioning any dimensions. The dimensions of the groove both radially and axially are critical if you wish to make an efficient seal. To get the correct size for an existing piece you can work back from the groove width and internal groove diameter. If you just want to stiffen a threaded part it's not near as critical. Not to mention backing rings .


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## RocketTomato (May 8, 2009)

wykeite said:


> Good job I read through the thread, it's more or less what I was going to say without mentioning any dimensions. The dimensions of the groove both radially and axially are critical if you wish to make an efficient seal. To get the correct size for an existing piece you can work back from the groove width and internal groove diameter. If you just want to stiffen a threaded part it's not near as critical. Not to mention backing rings .



In my experience, I have found that a lot of o-ring grooves are not cut to spec on flashlights. But then again, as you said, it is not really a critical application.


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## dfemmert (May 7, 2015)

I didn't know there were so many materials used in o-rings. I just got a few inexpensive cree LED's and the o-rings are about +/-1.mm thick. They all stretch about 50% of the original diameter. Some are red, some black. I checked out a couple links posted here and it's pretty confusing.

I thought I'd replace them with something a little better. I just looked at several sizes at FastTech and they're all silicone and most are 1.mm to 1.5mm thick which will work. I'm not sure how much silicone o-rings stretch. Should I just get them with the I.D. a couple mm smaller than the dia. of where they'll be going. 

I'm not sure how well silicone handles heat. The one on the bezel is the only one that'll get warm and that shouldn't get too warm with my use. My biggest LED's are the XML T-6 with 3100mah to 3400mah Panasonic ncr18650b li-ions.

I did find this chart that gives me a better idea of what to expect from a t-6. I've read enough to know not to pay much attention to the lumens that are posted with Lights from China web sites. XML T-6 LED's are said to have anywhere from 500lm to 2000lm. I don't want the heat from a 2000lm, I'm satisfied with 600 to 800lm and longer battery life. 
So much for posting the LED chart from my pictures folder, you have to enter a URL...I'm not that computer savy.

Thanks for any info.
David


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## magellan (May 7, 2015)

Yes. And be aware neoprene O rings are different in that you can't use petroleum based lubricants with them. The rings can swell and make it difficult to unscrew the cap or head.


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## dfemmert (May 8, 2015)

I learned long ago when I got into r/c cars, planes with plastic/nylon parts/gearboxes with bearings that silicone doesn't attack plastic so I planned to use silicone shock oil or better, silicone differential grease on the tail cap and bezel threads. 

On my focusing lights, the head slides forward and back and they slide better when you turn the head as you push or pull it back but this tends to unscrew the head from the body on a couple of them. I thought about using a little thread lock on these threads.


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## dfemmert (May 8, 2015)

After a lot of reading it's said not to use silicone oil on silicone o-rings. I saw several threads here on CPF and it's confirmed though said that it may not be that important for this application, it's more important where o-rings are used under pressure as in hydraulics...
I was considering the use of diff grease I have for r/c car diffs but it's too thick. I have silicone shock oil for r/c shocks. It comes in different weights (thickness), I have 20wt, 30, 35 to 50wt and I'll use the latter until I replace my o-rings. 
I can use my silicone oil but will need to go back and check some links to find a source for Buna-N (nitrile) o-rings which are safe with silicone. 

If I get silicone o-rings, the best lube I've found for them on CPF is Nygel 760G. $20.00 for a 57g tube at batteryjunction. 
"It's a silica thickened, medium viscosity, synthetic hydrocarbon grease used to lubricate and protect electrical contacts. A dab on the threads & o-rings of your flashlight will protect it from the elements and water." Good stuff but a little expensive.


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## dfemmert (May 8, 2015)

magellan said:


> Yes. And be aware neoprene O rings are different in that you can't use petroleum based lubricants with them. The rings can swell and make it difficult to unscrew the cap or head.



I'm thinking about getting Buna/Nitrile o-ring at smallparts.com. How much does a Duro 70 stretch? I just need them to stretch down over the threads into the groove below the threads on the bezel and tail cap.

To go in a 16mm dia. groove they have a 15mm(ID) x 1mm, for a 23mm they have a 22mm x 1mm. Is going 1mm smaller going to be tight enough or should I get them with a 2 or 3mm smaller ID?

The o-rings that came on them are like rubber bands, the o-ring that's in the 31mm groove on the bezel has an ID of 17mm.


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## savumaki (May 8, 2015)

underwatermike said:


> Use nitrile (buna-n) or viton. Either will work. The important thing is to get the proper interference fit. A minimum interference fit of .010 and a maximum fit of 0.28 is the range to work in. The Parker seal catalog is the standard reference on this.
> 
> The 70 durometer O-rings should work just fine. 90 durometer will work also, but will be harder to assemble.
> 
> ...



I worked for Parker at one time and I would say Viton covers all the bases.


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## nbp (May 8, 2015)

Buna (nitrile) or Viton are great options as the resist everything, wear slowly, and are cheap. EPDM breaks down and gets gummy with some lubricants, so I don't like it. Silicone can't be used with silicone, and it's more expensive. Fluourosilicone are cool and blue but only good for decoration; they are very expensive and they are pretty soft. PTFE are hard and cannot be stretched. Those are some of the ones I have experimented with. I'd just go with Viton and be done with it.


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## dfemmert (May 9, 2015)

Thanks for all the info, I found metric Viton V75's at the o-ring store. 1mm x up to 25mm ID. I need a few 31mm which they have in 1.5mm and the 1.5's are about 1/2 the price of the 1mm so I'll try them. It may be a little snug but it's on the bezel so it won't be getting screwed on/off all the time like the tail cap.

After researching some terms in the post by underwatermike, he mentions the "max interference fit is .28" which is 7.112mm. If that's the maximum you want to "stretch" them, I'll get them 2mm smaller than needed. That should give me a snug fit without excess stress on the o-ring.


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## precisionworks (May 10, 2015)

FWIW here's an unscientific test of Buna-N O-rings ...

I machined the Ti-6-4 shifter peg (below) for my H-D Road King. The Ti cylinder is grooved & Buna-N O-rings were installed as shown:







After less than 12 hours of outdoor exposure there was visible cracking on all O-rings. Then they started to break. Removed the remaining ones & installed silicone (red) O-rings. Can't detect any deterioration after 24 hours use & cost wasn't much more than Buna-N. 

FWIW #2 ... I believe that McGizmo installs silicone O-rings on all his titanium lights. I use either Krytex PTFE grease or NyoGel 760G (which contains silicone). No O-ring issues on any McG lights & some are over 8 years old, still using the original O-ring. 

FWIW #3 ... Jason (DarkSucks) includes silicone O-rings with his more expensive lights.

All of which leads me to conclude that maybe they're OK :nana:


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## nbp (May 10, 2015)

Barry, 

McG's old lights like the PDs used the red silicone rings, but he has been using EPDM on the newer models for years. Popular lubricants like Nyogel eat the EPDM. Grrrrr.

Jason uses nitrile rings on the Ready Mades and uses the blue fluorosilicone rings on the more expensive models. Not silicone. 

Also, your peg experiment has me curious. I have a bunch of buna-n rings I purchased for my McGs - I will put some outside to cook. My supposition is that those were either overstretched or already dry rotted or you had some nasties on your boots from the shop that killed them. A half day in the sun should not destroy o-rings of any flavor as far as I can tell.


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## Yoda4561 (May 11, 2015)

Anything petroleum based will eat EPDM quickly( most "synthetic oils" are still petroleum based as far as EPDM is concerned). On the upside not much is as weather or solvent resistant (acetone/MEK) as EPDM. Silicone and krytox work best for EPDM as lubricants. I'm not sure about how EPDM reacts to extended exposure to skin oils though. There's a reason they make O-rings in so many different kinds of polymers, every one of them has an application they work best in. For a dive light or car painter EPDM will work great due to the water/hot solvent resistance, for a mechanic's light Buna/viton would be best since they work fine around most petroleum products like motor oils and parts washers.


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## precisionworks (May 11, 2015)

nbp said:


> ... McG's old lights like the PDs used the red silicone rings, but he has been using EPDM on the newer models for years.


 That shows how long it's been since I've purchased a McG. I wasn't aware ...



> ... Also, your peg experiment has me curious. I have a bunch of buna-n rings I purchased for my McGs - I will put some outside to cook. My supposition is that those were either overstretched


The O-ring size is -210 (3/4" ID x 1" OD x 1/8" wide). The peg groove diameter is .800" & generally a 5% stretch is acceptable. These are stretched 6.6% so that might be one factor. 



> or already dry rotted


Brand new in sealed package.



> or you had some nasties on your boots from the shop that killed them.


I never wear work shoes on the bike. And the shifter pegs are contacted only when shifting, a small percentage of total time on a highway ride. 

Not sure why but the red ones still look like new & they are sprayed with silicone each time the bike is cleaned.


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## NoNotAgain (May 11, 2015)

precisionworks said:


> FWIW here's an unscientific test of Buna-N O-rings ...
> 
> I machined the Ti-6-4 shifter peg (below) for my H-D Road King. The Ti cylinder is grooved & Buna-N O-rings were installed as shown:
> 
> After less than 12 hours of outdoor exposure there was visible cracking on all O-rings. Then they started to break. Removed the remaining ones & installed silicone (red) O-rings. Can't detect any deterioration after 24 hours use & cost wasn't much more than Buna-N.



Buna-N is **** poor in regards to UV light resistance.

http://www.marcorubber.com/material_chart.htm

Viton is a trade name for a Fluorocarbon type rubber product. It possesses excellent resistance to hydrocarbons (fuel system parts) and UV light. 

The materail with the best chemical properties typically doesn't win out in a down select. It's the product with the lowest overall cost verses physical properties that takes home the cake.

If you want an all purpose lubricant that can be used on all types of o-rings, try Boe-Lube. Works well for drilling, milling, turning and brass case resizing. Oh, and non-toxic.


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## precisionworks (May 11, 2015)

NoNotAgain said:


> Viton is a trade name for a Fluorocarbon type rubber product. It possesses excellent resistance to hydrocarbons (fuel system parts) and UV light.


Interesting, cost is only slightly higher than silicone. McMaster sells 50 -210 silicone for $10.17 & 50 of Viton A for $12.76.



> ... uses the blue fluorosilicone rings on the more expensive models.


Those are pricey, five cost $8.38 at McMaster. May give those a try when the silicone rings need replacement as the blue is a better color match for the paint on the bike 

All things considered, EPDM might be the best choice ... or not. I found 90 duro viton rings on Amazon & will try those next.


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## precisionworks (Jun 14, 2015)

precisionworks said:


> ... I found 90 duro Viton rings on Amazon & will try those next.


They are the ticket

Harder than heck to stretch on but so far they've worn like iron. Almost 1,000 miles of shifting have left no visible impact.


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## nbp (Jun 14, 2015)

nbp said:


> I'd just go with Viton and be done with it.





precisionworks said:


> They are the ticket
> 
> Harder than heck to stretch on but so far they've worn like iron. Almost 1,000 miles of shifting have left no visible impact.



:thumbsup:


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