Quality of bolts.

[pandos]

I understand that the grades of bolts is often marked on their heads and in simplistic terms, the higher numbers correspond to stronger bolts.

I am rebuilding my engine, many rusted bolts that I fully expected to shear off as I removed them came out after exerting considerable force on them.

I have no doubt that if these were ordinary bolts , bought over the counter at the local hardware shop, that they would have sheared.

So I am wondering is there a rating system for the quality/durability of bolts. Are there manufacturers or suppliers who are respected for their quality, more than others.

I intend to pick up a supply of new random sized metric bolts and nuts for reassembly. (Obviously I will be using proper cylinder head bolts).

I have used black Japaned bolts from a local supplier in the past which always seemed to be better than the silver passivated/galvanized ones that are generally available. Is this likely to be just imagination on my part?.

 

[vyv_cox]

Steel bolts, whether galvanised or not, use a simple strength designation marked on the head. For example, the first digit in an 8.8 is the strength (UTS) in megapascals divided by 100 and the second is the yield strength as a proportion of the UTS. These are the lowest grade of what are described as high tensile, sold by Screwfix and many others. More specialised bolts can be bought, e.g. 10.9, 12.9. Few engines need better than 8.8. Most bolts in non-critical duties are lower again, 4.6 or 6.8.

Stainless mostly come in relatively low strength, equivalent to the first digit above but not marked. These are 50 ( UTS in megapascals divided by 10.) Superior strengths are marked 70 and 80.

Google Image Result for https://www.fastenerdata.co.uk/media/wysiwyg/technical/metric_tensile.JPG

 

[NealB]

This ties in nicely with my post yesterday (about bolts for mounting sheet winches).

Does anyone know if M8 countersunk stainless bolts are easily available in A4 - 80, please? I've tried a couple of places, but their bolts are A4- 50.

 

[alahol2]

A4 - 70...

 

[Neeves]

Tensile strength is no indication of corrosion resistance. Its not relevant but tensile strength and abrasion resistance often correlate - but not so corrosion resistance.

You can, relatively, easily source Class 8.8 galvanised bolts (in Australia) but I'm not sure that you can source galvanised bolts, easily or at all, with significantly higher tensile strength.

You can source Duplex or even better, Super Duplex, high tensile (stainless) bolts. But you may find them difficult to source and very difficult for your wallet to open.

If you are looking for corrosion resistance then maybe greasing the bolts might be the cheapest option - but then any sealant will not adhere.

If you demand HT galvanised bolts better than 8.8 look at sheradized bolts or TDG (thermal diffusion galvanising) Finished (Plating) - I shudder as I think they may be seriously expensive. I come across TDG bolts, monster studs, with seriously high tensile strength as they are specified to hold up the pylons for wind farms.

Jonathan

 

[pandos]

Thanks for the replies...I think I have not made my self clear enough.

My question can be rephrased...are all 8.8 bolts created equally in terms of quality, not just in terms of claimed strength? and are there respected suppliers whose 8.8 bolts would be expected to perform better than others.

I am not looking for corrosion resistance per se. I was noting that some bolts that had significant loss of body to corrosion still maintained sufficient integrity to be unscrewed, requiring considerable force, without shearing off...

 

[stone beach]

Not sure what measure of quality you would wish to use, all fasteners are definitely not created equally !! anyway, to try and be helpful, I have found these people to be good suppliers of fasteners for my personal use :-
Nuts and Bolts, Screws, Fasteners and Hose Clips - Westfield Fasteners Ltd

 

[penberth3]

.....My question can be rephrased...are all 8.8 bolts created equally in terms of quality, not just in terms of claimed strength? and are there respected suppliers whose 8.8 bolts would be expected to perform better than others.....

It's a good question. As with everything else, there are dodgy imports. They might be marked 8.8 but they are below that strength. All you can do is buy from a proper supplier, not the cheapest you can find on Ebay.