They are aluminum, and come with an assortment of mounting bolts and adapters, all of which I didn't use. Instead, I put some new holes in the brackets and used some self-tapping sheet metal screws in a #14 size:
These have a length of 1-1/4" but the 1" screws would be plenty long. Installation was relatively easy, short of getting the first hole drilled. And make sure you have a proper magnetic drive bit to match the screws if you attempt this - it will make it go much easier.
UPDATEI've since discovered from a Promaster forum that there is a different version of this step (different manufacturer) with a mounting bracket that looks much easier to install:
It also appears to stick out more, meaning you can get more of a foot on it. This may be a better option than what I did.