Who makes the best 24/40 (or other joint size) to KF25 adapters? Or what material is best?

So there are 3 main styles I’ve come across: PTFE, stainless, and glass. From what I’ve gathered the PTFE ones, while being the most common, are the most liable to vac leaks.

I’ve heard stainless to glass is not ideal. Is this true? Why is that exactly?

Am I correct to assume that glass is the way to go?

As I understand,

pros: cheap, durable
cons: leaky?

pros: durable
cons: ???

pros: unlikely to leak?
cons: fragile?

I hate the PTFE ones for anything even remotely warm. But that’s what we use. Maybe stainless with a PTFE sleeve would be superior as the sleeve might squish a bit

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Ptfe hot connections. R place every so often.

Stainless can be used on the colder or room temp connections.

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its about thermal expansion.

steel and glass expand at different rates.

as soon as the steel 24/40 side of the adapter gets warm it will expand braking the female
glass socket on your flask.

It is possible to weld/blow metal onto glass but it takes a very tallented glass blower and a lot
of money.

first they make a lead glass that is attached to the boro fitting.
this is then platted I believe and then that plate is then plated and so on till you get to
the metal that you wish to use as your base to fix the other metal part to.

again you will find thermal expansion problems with this.

for me the best in all glass is schott.


Seem some really nice ptfe ones from lab society. Spendy though.

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If they have orings then the material type doesn’t really matter too much. No reason why PTFE would leak anymore than metal or glass. It’s more about machining to spec. PTFE does deform somewhat under load and has very little elasticity so they don’t seal the best by themselves but the oring will do the trick.

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Ptfe can be machines to high tolerances. They say ptfe only fits perfect the first ten times. This is because it has memory and becomes malliable under temp. Just removing it changes it’s shape of you aren’t perfectly straight. O ring style joints are made with orings bc they leak and made from extremely cheap stock.

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