Sea cocks: Bronze or composite?

Are there different qualities of bronze like SS?

yes, that was my point. But how does one determine the grade except by manufacturer?

Here, the manufacturers widely recognized as the best for this stuff are Maestrini and Guidi.
Hard to name the absolute best, since both have their strength, depending on the specific product.
It's just worth mentioning the innovative "non stick" valves recently introduced by the latter, with no steel ball.
I heard nothing but praises about them so far, but only time will tell for sure.
If and how easily they can be sourced in the US, I really don't know.
Pretty expensive stuff even when sourced factory direct, anyhow.

Good point, I wasn't paying attention to that.

@ JohnHansen:
aside from what you can find directly in DK, I'm pretty sure that you can source the whole Maestrini range from the online chandler SVB.
You can't go wrong with their stuff.

Btw, I forgot to mention that when it comes to composite vs. bronze, I'm also in the bronze field.

I remember reading about a US valve mfgr sourcing their valves in China. They had major problems with corrosion, our last boat had them. I think Apollo was the brand.

I think you ignore composite valves and thru hull too quickly
check the NZ manufacturer https://www.trudesign.nz/marine/products
I know yachts that used these cocks for more then three years and they work smoothly like new !
by the way, it doesnt matter of sea cock material you use,
its good practice to go over all the seacocks once a month or two and move then on/off
i do it on my yacht with excelent results

+1.

In fact, when I decided to replace the mains seacocks in my current boat after purchasing her (when she was already 13 years old), I did check out also composite parts.
But back then - and I don't think the product range has been extended in the meantime - the max size available was 2".
And while my boat is no superyacht by any stretch of imagination, I needed 3".

That aside, also in my experience good quality bronze stuff, properly grounded, work just fine.
So, any alternative is actually a solution to a problem that I don't have.

Btw, menkes, lasting three years in perfect conditions ain't such an impressive result, to be honest.
I've seen 30 years old boats where the original bronze fittings were replaced to stay on the safe side, cutting in half the old parts afterwards out of curiosity, only to find out that they could have lasted another 30 years...
Though arguably that kind of bronze quality is harder to find, these days.

I'd replace them. I prefer Guidi over Maestrimi, Maestrimi's sea strainers and their baskets (I know unrelated to the thread) are the worlds biggest POS's.

I deal with a new Sunseeker right now that has over 1/2 of it's seacocks out of plastic and the remainder in Bronze, the plastic ones don't freeze or get stiff, but just working them, they flex a lot more than I'd like.

You are making me curious, on which boat(s) did you come across them?
They are pretty rare also among Italian builders - at least the half decent ones, which invariably use Guidi for strainers.
Not that I'm aware of any specific flaw in those built by Maestrini, but pretty sure the Guidi ones are built like a brick sh!thouse.
Coming to think of it, I can't remember to have ever seen a boat, no matter how old, where they had to be replaced.

Both, new Princess and Sunseekers use the Maestrimi's with the tiny criss cross holes/slots in the strainer baskets for the air conditioning strainers that you have to brush for half an hour with a tooth brush to get clean. The lid O-RINGS are garbage also and always swell and fall out of the little groove they sit in.

Some sort of Marelon sea cocks. The handles or body flex on all of the Marelon seacocks from what I've seen.

Exactly why I prefer bronze thru hull components. No corrosion or electrolysis is tempting but plastic is not as durable as bronze. Maybe ok on other plumbing but not thru hulls.