Topic: bolt strength question...

[amattel]

I was out bolt hunting today at the hardware store.

What are the practical differences between a bolt stamped 8.8 and one stamped 10.9?


thanks,

Adam

[amattel]

This is an m8 x 75mm x 1.25 pitch

these numbers (8.8 and 10.9) Refer to the metal the bolt is made from....  I am just not clear about what it means in a practical sense....

Any metals experts out there who understand the difference?

thanks,

Adam

[scunny]

steel grade 8.8---Made from medium carbon steel and zinc plated. Best for general hardware use where high strength is not required. Standard metric thread pitches
steel grade 10.9---Made from alloy steel quenched, tempered, and zinc plated (usually yellow). Best for automotive use and other areas where high strength is needed.
hope this helps

[Noel]

8.8 is medium carbon steel, quenched and tempered. Yield strength should be 92,000 PSI and tensile strength should be 120,000 PSI.

10.9 is alloy steel, quenched and tempered. Yield strength should be 130,000 PSI and tensile strength should be 150,000 PSI.

< edit > Oops, scunny beat me to it.

[Clyde]

This a brief explanation (which supports Noel's posting).
The numbering system is an ISO standard and slightly different to the American grading system
The numbers are used to calculate the tensile and yield strength of a bolt.
They work in mpa instead of psi, as the numbers use metric units.
The 8 refers to an ultimate Tensile strength of 800mpa which is roughly equivalent to 120,000psi. The second 8 is used to give the yield stress and is calculated by multiplying the two numbers together (8X8) and then multplying by 10 to give 640mpa or 92000psi
Check the following site out as it gives a better explanation
http://www.obex.co.za/data4.html

A even better site which gives both the ISO and American gradings is
http://www.boltdepot.com/fastener-information/Bolt-Grade-Chart.aspx
Regds
Clyde

[78CB750F1]

If you can afford the difference in price, choose the 10.9, especially for nuts and bolts that are under load.  My father used to prepare race cars - the first thing he did was replace all the hardware he could with 10.9.

[mrbreeze]

Great post !! I printed this and highlighted the sites that Clyde listed.Should go to FAQ .I don't know what catagory it should be in though.

[SteveD CB500F]

General FAQ !

[amattel]

Thank you so much! 

One more question.

The other choice I had when choosing a bolt was whether or not it was flanged.

I believe this means the washer-shaped section which extends beyond the edge of the hex head.  It seems like this would add more stability and strength, but what is the official benefit/use fo this?

thanks,

Adam

[dusterdude]

essentially.the flanged head replaces using a washer separately.it also spreads the load better against what you are tightening up.