A2 or A4 (316)?

[JawsOrca]

I ordered the bolts from the manufacture of the sterndrive to bolt the transom plate onto the hull and i'm surprised to see that they have sent A2 stainless bolts.. I at least expected A4 (316) considering they will be underwater... Am I wrong and A2 is OK to use underwater?

 

 

[Hockham Admiral]

Alan, Hi.

I've just read quite a few pages on this topic..They all agree it must be A4 because of the molybdenum (2-3%) that's added.

 

Here's one you might like to peruse:

 

http://www.canalworld.net/forums/index.php?showtopic=51126

[JawsOrca]

Thanks John (sorry .. I found that too.. It's the salt bit of the broads which I thinks complicates things.. although I had a big long chat with the chap about the boat being in brackish water although he still sent A2 so I'm hoping he knows more.. I think I'm going to send back though and get A4.. piece of mind.. 

[JawsOrca]

I need to stop panicking (I need a holiday!)...  They company replied stating that A2 is far less reactive than A4 and would be fine (as they have been since 1969!)...

[MBA Marine]

A4 is better, A2 will cause you no problems, apart from one, avoid A2 nuts as the have a habit of seizing on the threads especially nylocks, they fuse solid and even the likes of a m12 the bolt will sheer before the nut lets go!  

[JawsOrca]

Brilliant, top tip.. thanks Mark.. appreciate that..   I must admit most of the nuts on this outdrive when we have tried to take it apart have done just that (I thought it was me!)..

 

[mbird]

A4 is better, A2 will cause you no problems, apart from one, avoid A2 nuts as the have a habit of seizing on the threads especially nylocks, they fuse solid and even the likes of a m12 the bolt will sheer before the nut lets go!  

 

Hi Mark

 

I know what you mean about stainless Nylocs. I detail structural steelwork for a living for the construction industry, and they prefer to use stainless self-locking nuts, which have a split crown rather than a nylon insert.

 

One question for you though, I thought I had read that A2 bolts were more prone to cavity corrosion than A4. Has that been your experience too?

[Guest]

A4 for me on boats, every time, especially when immersed.

 

I rarely use A2 even at home now, because it also has a very frequent problem with welding itself up tight due to "reaction" when first being threaded together .

 

Something that never happens with A4, or even mixing A4 nuts with A2 bolts or vice-versa.