Fifty {Two} Shades of Grey - Week 30

Another one for the crafters or builders out there... if that's not a big hint then I don't know what is.

It's kind of obvious if you look closely, squint your eyes and get the laptop screen just so... and then sort out the lighting because I've intentionally shot this photo so it looks darker than it is in reality...

Why it's two metal rulers of course. Though I was being tricky by putting more than one in the picture and adding the reference to builders... did it work?