2xcapeIN

Honestly depends on what kind os steel it is( trust me there are differences) anyway 7018 WOULD give you good penetration! Oh and dont forget to ground out as close to your work as you can. You don't want any bearings ect... getting welded also.
example; I was welding on a lawn mower and ruined the engine(welded internal parts) cuz I grounded out at the opposite end of where I was welding.....lesson learned!

MD5

I learned to always attach the ground close to the work area but I tough because this can help in optimizing the weld process or avoid damage to electrical car circuit even if the battery is disconnected.
I'm impressed that keeping the ground far from the work area could cause such serious damage!
This is an extremely good thing to know, thanks for sharing!

ironworkerlu21

7018......3/32

stronger then a 60 series rod, and a nice small diameter for running off of a small output welder. I've used it alot on handrail.

Or if that's not available try, p5, it's red in color. This is a pretty easy rod to run, if you don't have alot of experience.

Serg5000

a welder that has experience should be able to look at the job and figure out what he is going to need. Just my 2 cents.