Jamesh wrote:...what's the other hobby btw???...
for many years (not so much these days) I have messed about with cars and motorcycles. In my previous working life I worked closely with various vacuum systems.
Foghat wrote:Has anyone got a source of stretchy o-rings?
Most o-rings that I've found are not very stretchy at all, but the ones I wish to procure a spares supply for are really quite stretchy, which is a very useful feature. The stretchiness does, though, mean they are somewhat prone to breaking.
The particular stretchy size I wish to buy a plentiful back-up stock of is 42mm ID x 2.5mm CS. The ID could be both several mm larger or smaller and still work, but the CS probably needs to be no more than +/-0.5mm.
Most 'O' rings are sold as seals and only need to be as stretchy as is required for the sealing application (which is not very), and chemical resistance is more important. My guess is that you are after rubber rings to retain lights etc to handlebars. I confess I don't know what rubber grades are used in these rings normally, but I suspect it might be mostly butyl rubber with (hopefully) a cocktail of additives which are intended to make it weather resistant (a bit like tyres). Whereas O rings seem to be (if not specified eg in cheap boxes/kits) most commonly made in Nitrile rubber. So when I have needed these rings, if O rings are not stretchy enough I've bitten the bullet and bought the right thing even though it cost more than I'd like.
Further to the original post above, I have discovered that at least one of my many boxes of cheap O-rings contains seals made in a rubber grade that deteriorates quickly in external conditions. The thing is, I'm not sure which box; I have used many O-rings from several cheap kits to replace the seals in PD-M324 and PD-M323 pedals; you need four at a time (for a pair of pedals) and I remember having to take three from one box and one from another. The 'odd one' perished in less than a year and the other three are still fine. Obviously I don't recall which box the rogue O ring came from.... Needless to say I'm now worried that I might have used (or will use) an O ring from that box (whichever it is) which might turn into a big problem.