A2 stainless coach screws OK?

[bluedragon]

Just bought some coach screws locally to attach S/S strips to epoxied wood (iroko). However I notice they are A2 not A4. They will be well sealed into the wood (don't want water getting in anyway) so only the hex head will be exposed on deck. Is the fact they are A2 likely to be a problem in the long term?

 

[alb40]

Re: A2 stainless coach bolts OK?

They should last a long time regardless. Most of the stainless gear in the local swindlery like screws are probably A2 grade anyway! You only really need to use A4 grade when they are used below the waterline.

Someone is likely to come and give some bull on corrosion, electrolysis etc. I took up my teak deck earlier in the year, which was fastned in stainless screws christ knows how long ago, and they were all still in perfect condition.

 

[srp]

Re: A2 stainless coach bolts OK?

Go to www.a2a4.co.uk - there is a link to an explanation of the difference on the first page. I met the bloke who runs this company yesterday - he seems really efficient, and has a huge range of fastenings of all types.
If you can get them I would really recommend A4 (probably not what you want to hear as you've already bought A2 !! ).

 

[Birdseye]

I spent a significant part of my working life making stainless steel wire to sell to cold headers who in turn made fasteners. So unlike some posters, I do know what I'm talking about.

In a salt laden environment, you should use 316 quality fasteners - A4 if you like using german designations. Even then, they wont do too well in wet wood because they will be shielded from the oxygen that maintains the protective surface coat. A2 screws will rot quicker than A4 and the bare head will stain. But if the wood is dry and the screw well buried / sealed, then there wouldnt be a problem with A2.

You should be careful of using A4 screws below the waterline. The exposed head of the screw may well do OK, but the bit of it that is burried in wood or GRP will suffer from the stagnant water round it. For example I once removed the 10mm A4 bolts holding the skegs on my Prout cat. The heads and nuts were OK, but after only 10 years and buried in mastic by Prout, none of the bolts was re-useable thanks to corrosion. Only half of them came out in one piece

There are more exotic grades of stainless that fare better, but if I were fastening down a wooden deck I would go for correct non ferrous.