Tensile strength of bolts

[slap_ed]

I need to fit longer bolts through my steering rack clamps due to raising the level of the rack. I'm having difficulty finding some 4" x 1/4" unf cap head bolts. I can get some standard hex bolts at this length but these only have a tensile strength of 8.8 as opposed to 13 for the cap head type. My question is how risky would would this be using this strength of bolt? Or does anybody know where I could get this ideal 4" x 1/4" cap head bolt from?

Cheers

[CharlesElliott]

I would be happy with 8.8 here. Or you could replace with M6.

[slap_ed]

Hi Charles,

So is this the metric equivalent to a 1/4"unf?. Will these go through the original rack clamp holes?

cheers

[CharlesElliott]

1/4" is 6.35mm, so an M6 bolt will fit, yes.

[Mankee]

I think I've got a spare set of new fixing bolts, washers and nuts from another club member when i had three sets of 9mm (or was it 9.5mm?) spacers made up to lift the steering rack. Let me know if you want them and I'll dig them out of the garage. From memory, they are just "normal" bolts. It's not as if the steering rack needs anything more than an 8.8 fixing.

[slap_ed]

Thanks Mankee for the offer. I already have the spacers, it was just the longer bolts I needed because I need to raise the rack a little further. 

I've found some M6 bolts on EBay and have ordered some.

thanks all.

[DaveMorris]

I'd be more tempted to use correct diameter 8.8 spec bolts rather than an M6 just on the basis that it fits thru the hole. Just feels wrong somehow.

Seem to remember there was a discussion on this last year sometime. D

[Stridey]

A higher number doesn't mean 'stronger'. The higher numbers may mean they are actually more brittle in usage.

 For example in skateboarding we use American Grade 8 bolts as kingpins, over the years I've seen a few higher graded number used, even titanium, but the grade 8s have a small amount of flex, allowing them to withstand shocks better. The higher grades tend to snap.

Obviously in something more safety critical like a car it's worth double checking what grade you should use, but assuming higher numbers or more fancy materials will be better in use than perhaps bog standard bolts might be a mistake.

[Steve_K]

 

Bolt strength isn't probably an issue here as the bolts clamp the rack to the chassis. The forces from the road to the chassis are reacted by the friction in the clamps so as long as the bolt can deliver the required torque, they should be fine. Brittle materials wouldn't be a good idea here.

Steve