What's the difference
 

looking at some rays lug nuts and i can't seem to see much difference between these 3 other than the price...

1. 35mm length, made from Duraluminum
http://www.evasivemotorsports.com/mm...tegory_Code=L1

2. Made from hardened steel
http://www.evasivemotorsports.com/mm...tegory_Code=L1

3. 42mm medium length, made from Duraluminum
http://www.evasivemotorsports.com/mm...tegory_Code=L1


1 and 3 look to be the same except for the length. Number 2 looks like the lock nut is different. Anyone know anything else?

Material, length and colour. You pretty much answered your own question. They would all work equally well if you need a tapered lug nut.

Kinda like the difference between your FRS and Tcoat's FRS.

Same thing, except maybe transmission type and color.

Are aluminium lug nuts really an option for our cars? I chose steel for mine, just because aluminium seems a pretty poor choice for a fastener that's holding my wheels on.

Happy to be educated otherwise. Would saving 275g per wheel be worth it?

If stock lugnuts are aluminium, imho that says that they are ok to use :).
As for if saving on lugnuts weight is worth it .. imho not. But i did it anyway. :D

The stock wheel nuts are steel.

That is where things get tricky.
Duraluminum is not "aluminum". It is an alloy that contains aluminum but is not of itself really aluminum. It can be as strong as or even stronger than some steel. Many aircraft components are actually made of the alloy.

"Hardened" steel although it sounds stronger is a pretty generic term that really means nothing as to durability and strength. Is it high or medium carbon steel? What method of hardening was used? What grade and level of hardening is the final product? Pretty much any steel that has been heated and quenched can be called "hardened" but that does not mean it is effective for the purpose.

Aluminum lug nuts *should* be either 7075-T6 or 2024-T6 aluminum, which are much stronger than 6061-T6 and as Tcoat pointed out stronger than some steel alloys.

"Duralumin" according to wikipedia is 2000-series aluminum, but Rays calls their aluminum "A7075" lug nuts "duralumin". They don't say they're T6 but surely they must be...

I would never consider 6061-T6 lug nuts, but 7075-T6 or 2024-T6 from Rays/Volk or other known good supplier are probably OK.

STill it's not much weight-savings, personally I would stick with good quality steel nuts.