A4 strength

[AngusMcDoon]

Is all A4 steel the same strength, or does it come in different grades? I have to replace an M10 bolt, and the application is fairly critical to the integrity of my boat. The old bolt is marked A4 but has no strength indication like good quality rusty steel bolts have.

 

[Momac]

Information on the following suggests stainless bolts are manufactured in different strength grades

http://www.bssa.org.uk/topics.php?article=1

 

[VicS]

also see http://www.roymech.co.uk/Useful_Tables/Screws/Strength.htm

 

[Sneaky Pete]

Stainless

Its 316 St St and it will not have the tensile strength stamped on it. All 316 is made to the same recipe, what is the bolt holding, replace it like for like there is always a factor of safety built into these things.

 

[AngusMcDoon]

So it looks like A4 does come in different strength grades, but I have no way of telling what grade the bolt to be replaced is. Makes it difficult to replace it like for like. Pity that SS bolts are not marked like rusty steel bolts.

The bolt attaches a beam hinge to the hull on my Dragonfly trimaran. It's one of 40, 10 per hinge.

 

[VicS]

So it looks like A4 does come in different strength grades, but I have no way of telling what grade the bolt to be replaced is. Makes it difficult to replace it like for like. Pity that SS bolts are not marked like rusty steel bolts.

The bolt attaches a beam hinge to the hull on my Dragonfly trimaran. It's one of 40, 10 per hinge.

If its not marked with a grade I think you will find its the lowest.

heavens knows where you'll buy any of the higher grades

 

[ripvan1]

contact manfacturers for spec sheet ?

 

[CelebrityScandel]

Pity that SS bolts are not marked like rusty steel bolts.

They are so marked - for example, A4 property class 70 bolts will be marked A4-70. If not so marked one can assume they are property class 50.

But for a critical installation just do as another has advised and ask the builder of the boat in order to be sure what is required.

 

[penfold]

They are so marked - for example, A4 property class 70 bolts will be marked A4-70. If not so marked one can assume they are property class 50.

But for a critical installation just do as another has advised and ask the builder of the boat in order to be sure what is required.

Also buy the fasteners from a reputable supplier who can offer some traceability, rather than some bloke off ebay(not that there aren't reputable traders on ebay, just 'caveat emptor').

 

[AngusMcDoon]

Also buy the fasteners from a reputable supplier who can offer some traceability, rather than some bloke off ebay(not that there aren't reputable traders on ebay, just 'caveat emptor').

The problem is finding a supplier who will sell just 1 or 2. I have found the part (of unspecified property class) from www.seascrew.com. At least they seem UK based and have a phone number, so I shall call them and try to find out if their products are made to any specification. Thanks for the advice from everyone.

 

[captainboo]

Try A2A4, they sell some A4 80 bolts.

http://www.a2a4.com/acatalog/A2A4_FULL_SELECTION_OF_HEXAGON_HEAD_BOLTS_53.html

 

[RestlessL]

or Westfield Fasteners

http://www.westfieldfasteners.co.uk/ScrewBolt_M.html

J

 

[vyv_cox]

I looked through my nuts and bolts collection on board, bought in a variety of chandleries between Holland and Greece. I was quite surprised to find many A2 and A4 -70 grades and even some A2-80 nuts. I had some good quality countersunk Allen bolts which were also labelled A2-70. The convention seems to be that the lowest grade is simply marked with the composition, higher grades with the strength. My collection suggests it is not difficult to find the higher grades.

 

[AngusMcDoon]

My collection suggests it is not difficult to find the higher grades.

What I have so far not said is that the offending part is a 45mm M10 carriage bolt. These are not so easy to find.

 

[AngusMcDoon]

Just spoken to Sea-Screw, and their A4 bolts are property class 70. He agrees with what has been said here that my broken bolt, being unmarked, will be a 50. He also said that buying an A4 class 80 carriage bolt off the shelf would probably be impossible anywhere and would have to be specially made if anyone wanted them.

 

[vyv_cox]

What I have so far not said is that the offending part is a 45mm M10 carriage bolt. These are not so easy to find.

But it does sound as though you are not looking for a higher strength one, which should make your search less arduous.

 

[AngusMcDoon]

But it does sound as though you are not looking for a higher strength one, which should make your search less arduous.

I'm not, but I started off not knowing anything about A4 strength grades. Having spoken to a supplier the fact that their products are marked with a strength grade gives me confidence that they are a quality assured product and not some nasty Chinese cheese metal thing from Ebay. I have now ordered the parts I require.