I want to get an assortment to tighten up some of my flashlights.
Any favorite place that you get yours from?
O-rings are used by plumbers so go to a plumbing supply house just get the ones you want. H)
OSH
Thanks.
How does one measure for size? The exact diameter of the flashlight part where the ring will be fitted? Or should the O ring be slightly smaller to ensure a tight fit? Is there a rule about thickness?
Thanks for the OP samsat, this is another of those Q's I've been meaning to ask for a looong time now :\
Lensman there is engineering freedom for designing o-ring grooves and choosing o-rings. Anything that fits is allowed. So the best way to replace o-rings is by measuring your existing o-rings ( inner diameter D1, outer diameter D2, that gives the thickness t = (D2-D1)/2 ) and buying the exact same size.
imho the o-ring (inner diameter) should be a little smaller to ensure a tight fit. yes.
signed. kreisler. the bada$$smarta§§ ;)
Good stuff bada$$smarta$$ BG I wwas gonna ask this Q today as well.
Keith.
I would have never thought plumbers would need such small O-rings. I have a friend that is plumber.
Keith (who will be able to gettum for nothing:)
Kramer sir, might I ask, "what is OSH?"
Keith
OSH is Orchard Supply Hardware not many of them around and not one close enough to me.
I see though that Home Depot and others carry them and there are assortments on Ebay.
The plumbers ones tend to be quite thick.
I just checked Harbor Freight's website, 397 metric O rings for $5.99 with section size ranging from 1.9mm to 3.5mm. They may also be a bit thick but you cant beat the price!
Amazon has an amazing assortment for cheap.
I take the parts in question right to the local hardware store and fit O-rings right then and there. The help all think I'm nuts anyway! 
Rich
http://www.mcmaster.com/#93135K31
There's a nice sample kit with a bunch of different sizes, and they're all silicone. You can also search for "o-ring" and get any size and material you want.. metric and inch based..
I'm a huge McMaster-Carr fan. They ship same day, ship for reasonable costs, and have a selection of "stuff" like no other company on the planet...
PPtk
I bought them from DX, as those from my plumbers' sets are all too thick.
The DX ones are 1,5mm thick, which is right for the flashlights I own. The problem is that the sizes listed on the DX site are not specified whether ID or OD, so I ordered a whole line of them.
Thanks everyone, useful stuff.
Auto supply stores carry o-rings as well. The ones suited for the newest refrigerants are very durable and oil-resistant.
any recommendation for particularly good (bright, long-lived, flexible) glow-in-the-dark O-rings?
I've spent quite a bit of time looking for a sample list of o-rings for some of my flashlights - and become VERY frustrated. Every kit i've looked out has very few or none that would fit our needs. DealExtreme has some but only a few. Most of the o-rings available in the US are in SAE - whereas we need Metric.
Kreisler's place is the first that actually seems to have almost all of the sizes we're in need of.
The only problem is that there're set up to do business in the EU and not the US and I can't even determine how to pay them in an easy way (like PayPal).
A PROPOSAL (in several parts):
1)I suggest that we solve the payment problem first. (Perhaps Kreisler would be willing to call them to discuss that issue?)
2)Then we could each order based on our specific needs.
3)Better yet, why not make up a CHART of flashlight types that includes the o-ring requirements for each of the lights. That would be a little bit of work - but we could share the burden.
4)The chart could be used in 2 ways:
A)It could obviate the need for all of us to buy micrometers and remove all of our o-rings to see what we're using. That way, we could assemble our infividual orders together with ease.
B)We could assemble a GROUP BUY that includes multiple quantities of all of the most common o-rings and make a deal with Kreisler's source for an assortment that would come closer to meeting our needs. (By the way, "the other forum" did, in fact, do just that years ago but they were principally interested in SureFire at the time and their Group Buy had only SAE sizes - not the Metric that we need.)
A FEW FACTS:
NBR (otherwise called Nitrile or Buna-N) is what we need, NOT Silicon (which is too vulnerable to various chemicals/oils). NBR also has the advantage of being the most prevalent and the CHEAPEST of all of the alternatives. Prices will vary rougly from $.01 to $.05. Just as important, we should be able to fulfill ALL of our needs from only ONE SOURCE! - and not have to chase around.
Take a look at the list of offering from Kreisler's source and you will be absolutely AMAZED!
The only information we need for each o-ring is the ID (inner diameter of the ring) and the cross sectional thickness of the o-ring. OD (outer diameter) is automatically calculated by ID plus 2x cross sectional thickness (or width of the rubber) and the OD measurement is often even ignored in the sizing lists for that reason. The only other variable is Durometer hardness. It is usuall either A70 or A90 but A70 is probably best for almost all of our needs.
Note that the only thing that I'm unsure about is just how strechable the o-righs are. In other words, should we order just slightly smaller than the particular tube that we want to cover - or do we order the exact dimension? Another variation of this question relates to the o-ring that fits between the lens and the crown. Many of us know from experience that this one should be exact or it is difficult to place in the appropriate position without some of it "sticking out" from under the crown.
LET'S DO THIS! A little work to assemble a chart of needs for all the common lights and we can put a GROUP BUY together that will save us all a lot of time and hassle (not to mention money). By the way, a GROUP BUY would not prevent each of us from ordering individually based on our own specific needs - those people would simply not benefit from the package discount.