Bolt grade?

[tzei]

Hi!

I´m little cofused about the markings...

Google didn´t help so here i go:

Need replacement for my wilwood calibers. The bolts in Q are those that fixes the caliber halves together. Only marking is " H-K" on the side of bolts hex (socket?) cap. How hard is this? Here http://www.precisionscrewandbolt.com/metric.htm
table indicates that it might be 12.9 grade. Is this the case?

Thanks

[breezeblock]

are the bolts you are after metric or imperial

[tzei]

Originally Posted by breezeblock

are the bolts you are after metric or imperial

Imperial

[Dave Brand]

Originally Posted by tzei

Only marking is " H-K" on the side of bolts hex (socket?) cap. How hard is this?

That's not a grade - it's the maker's name, Holo-Krome!

See:

http://www.holo-krome.com/

I can't find my Metric Holo-Krome selector, but, from an old Imperial one, mechanical properties for screws under 3/4" dia are:

UTS 170,000 lb/sq in
Yield strength 150,000 lb/sq in
Elongation 12% in 2"
Shear strength 105,000 lb/sq in
Hardness 38Rc

[breezeblock]

for critical things like brakes i always use 12.9 or imp equivilant.some times manufacturers put cheap bolts in so always go for as best a bolt as you can borrow

[tzei]

Hard bolts it is then. Ok
Thanks everyone.

[THR]

the black ones basically.. if they tin plated they lower spec..
ifin doubt ask the manufactuer, they normaly dead helpful and wont make u feel stupid!!!

[tzei]

Originally Posted by THR

the black ones basically.. if they tin plated they lower spec..

This is my understanding also. My orginal bolts from calibers are tin/grey colored... but on holo-krome´s site there also "zinc with clear cromate" bolts that meets asme b18.3 and astm a457. This astm a457 is about the same as metric 12.9? So hard bolt can be other than black (which is normally the case)?

[breezeblock]

at our work it doesnt matter whether they are black or plated they still break them

[Dave Brand]

Originally Posted by THR

the black ones basically.. if they tin plated they lower spec..

Not necessarily - there are all sorts of anti-corrosion treatments which can affect the colour. Better to rely on markings on the head!

[djinvicta]

As a seller of nuts and bolts, what you have is an Imperial Socket Head Cap Screw, Grade 12.9, if Zinc plated it has to be dembritalled to keep its hardness. Weve got tons of them if you want any, and Ill certificate them too if needed, free delivery in the UK. Ring Dave on 01227 720020 daytime.

[275 GTB-4]

Go Grade 8....

[tzei]

Originally Posted by djinvicta

As a seller of nuts and bolts, what you have is an Imperial Socket Head Cap Screw, Grade 12.9, if Zinc plated it has to be dembritalled to keep its hardness. Weve got tons of them if you want any, and Ill certificate them too if needed, free delivery in the UK. Ring Dave on 01227 720020 daytime.

Thank You for help. I´ll try domestically first.

275 GTB-4: why should i go with lower grade?

[275 GTB-4]

Originally Posted by tzei

Thank You for help. I´ll try domestically first.

275 GTB-4: why should i go with lower grade?

You should not....so long as the plating has not embrittled the metal....

ARP and Grade 8 go well for domestic engines etc

[kmsport]

Zn plated Gr 8 bolts....2hrs in the oven preheated and maintained at 150C....good as gold!