Wazzzer

what shear rating are high tensile or stainless bolts?

I'm after some allen head M8 bolts for my strut brace and all I can find are either stainless bolts or high tensile but they don't say the ratings of them (in terms I understand anyways)

Turby2

Your allen head screws (cap screws) should be marked and are usually 12.9 grade. Standard 8.8 grade is more than enough.

Under stress stainless has a tendency to snap whereas steel is more "elastic".

You could use some nice titanium ones

Wazzzer

so stainless is a no no then?

I've got the OE nuts they use on the Audi S3 but the studs were already fitted to the strut tops so I've got to find these.

The frustrating thing is I only need 6 of them and most places want to sell me shit loads of them. Anywhere you know I could get 6 M8 x 25s for a good price

Mark V8

iTrader: (2)

I can't see a strut brace creating enough force to sheer stainless bolts.

These people sell small amounts and take paypal

http://stigfasteners.easywebstore.co...ead_A5MFR.aspx

Mark

NEEDFORSPEED

got all mine from brm engineering think they have a web site too il have a look the allen head bolts i got were only about 25p each in black 8.8 or 12.9

Wazzzer

I'm after black ones too M8 x 25 or 30

If you've got any info it would be much appreciated

PAUL S

iTrader: (8)

screwfix sell them cheaply enough

Wazzzer

just looked, they only go up to 20mm in the M8

Wazzzer

just had a look and the nuts are 8 rated so I'm thinking all I'll need is bolts to match these, am I right?

Also found out that stainless bolts have roughly 85% of the strength of an 8.8 rated bolt so that would make them 7.48.

"The vast majority of stainless fasteners listed on this site are grade A2-70, and have approximately 85% of the tensile strength of grade 8.8 steel bolts. As such, stainless fasteners are only recommended for non-stressed applications, which effectively rules out brake calipers, suspension mountings, brake discs, seatbelt anchors and propshaft bolts"

NEEDFORSPEED

il be going to get some more in the wk at some point mate so il grab some if you want then just send me some money for postage. how many do you need? absolutely correct about the stainless btw

Wazzzer

you're a star bud

I'm after 6 off M8 x 25 (or 30s if no 25s) socket screws (allen headed bolts)

Let me know how much I owe ya bud and I'll sort it out

Oh I take it they are the black natural finish and not zinc plated? Can't believe the coating process weakens them!

richm

8.8 will be more than sufficient for a strut brace, most steel socket caps will be at least 10.9 anyway. Zinc plating doesn't weaken them as such, they just go through another process to destress. A 10.9 rated fixing is 10.9 irrespective of plating etc. Don't forget that black ones will go rusty if that is an issue to you.
The function of a bolt is purely to provide clamping force between two surfaces, they shouldn't be under shear stress to speak of at all. The bolt should clamp the two surfaces together to provide sufficient friction that the two components won't move with respect to each other. Clearly if the two components experience higher loads in a particular application, they need a higher clamping force to hold them together, hence higher tensile fasteners to be able to provide the increased clamping.
The clamping force available from a M8x1.25 8.8 grade bolt is huge - 1000Newtons or so...

Wazzzer

cheers mate, useful info

I want the socket caps so I have a bit more room inside the strut to tighten them up

Didn't know black ones will go rusty, I'll stick some paint on them when they're fitted

richm

the blacks usually come in an oiled finish to stop them rusting in storage, so you will need to degrease them if you intend to paint them.

NEEDFORSPEED

no probs il get em sorted. mine went rusty and had to paint them!

richm

In practice you are unlikely to get any problem in this application with Stainless fasteners of a suitable grade:

A2-70 stainless is 85% tensile strength of 8.8 steel, A4-80 is 97%

Useful Stainless data here - http://www.anzor.co.nz/?t=30

It's not a safety critical application (unlike suspension or brake mountings) so if for some odd reason you do get a failure it's not going to kill you

WD Pro

http://www.geocities.com/dtmcbride/h...den/bolts.html

Just been discussing the same on another forum

The best would be 12.9's zinced and then de-embrittled will look nice with no worry of breakage and little worry of corrosion

For info my strut brace has been on for 10 years - stainless bolts - no problems