Hardware grades

[craigthefabricator]

I went to the local Tractor Supply (as suggested) to purchase most of the bolts, nuts, and washers for the build. This turned out to be a great deal, as you purchase everything by weight....doesn't matter WHAT it is - bolt, washer, nut, whatever... you can mix it all in one bag if you want and they just weigh the whole thing and calculate the price. Easy enough.

One thing that I was not so certain about was the fact that they offered items in 3 different grades: Grade 2 (silverish color that you usually see at your hardware store), Grade 5 (blackish color), and Grade 8 (yellow to greenish tints). The higher the number, the "better" the hardware presumably.

What I don't know is what grade is sufficient/appropriate for a CNC build such as this. Also, I was unable to find sufficient quantities (or any quantities in some cases) of some items in a particular grade, so I ended up having to buy across all three grades.... though MOST of the items I got were Grade 8....though the carriage bolts were only available in Grade 2 (and, at that, only sizes ABOVE 1" - will have to source the shorter bolts elsewhere).

So, aside from thoughts on the appropriate minimum grade, does it hurt to use a higher grade (other than a slight premium in the price)? And, can you mix and match items from different grades? Say a Grade 8 bolt with a Grade 5 or Grade 2 nut (setting aside the fact that the weakest link in the chain is going to be the point of failure)? Since I don't know what makes up the different grades (different alloys? different heat treatments?), I don't know if using various grades in a single connection will have issues with differing thermal expansions, chemical/oxidization interactions, and so forth.

Would appreciate thoughts from anyone who knows more about this stuff than I do.

Thanks!

-craig

[msimpson]

Any grade will work just fine.

[JonPaulJones]

ybe this will also help answer your question from an engineering point of view:

Determining Bolt Grade

Bolts of different grades are marked on the head to show what grade bolt they are.

Grade 2

Grade 2 is a standard hardware grade steel. This is the most common grade of steel fastener and is the least expensive. Grade 2 bolts have no head marking (sometimes a manufacturer mark is present).

Grade 5

Grade 5 bolts are hardened to increase strength and are the most common bolts found in automotive applications. Grade 5 bolts have 3 evenly spaced radial lines on the head.

Grade 8

Grade 8 bolts have been hardened more than grade 5 bolts. Thus they are stronger and are used in demanding applications such as automotive suspensions. Grade 8 bolts have 6 evenly spaced radial lines on the head.

[msimpson]

Thanks for the information.

Grade 2 will be fine. Thats not to say that if you have a lot of grade 5 laying arround, you could use that.