These icons were found at wearequeue.com for a company called Hardhat Creative + Consulting. They were created by Chad Martin, whose work can be found here. An episode of Cory Kerr's podcast "illo talk" with special guest Kyle Adams is referenced in this post. You can find that episode here.
Reverse Engineer Post
Hardhat Creative + Consulting
Emphasis
Kyle mentioned during the podcast that when you go to make an icon set, you need to think about what you want to achieve with the icons. You shouldn't go in with zero goal in mind or without any purpose. The purpose can be shown by giving something in the set emphasis. This half of the icon set has a clear emphasis on hard hats, which you can see clearly because they are yellow against the other neutral elements of the icons. That makes it obvious that the set is related to construction in some way.
Contrast
Yellow is the only contrasting color used against black, gray, and white which makes certain parts of the icons pop. Everything that would be realistically be gray is gray, and vice versa with the yellow. Also using yellow and gray in the same single icon makes the icon more interesting and gives it more meaning (example: a yellow gear is a bit plain, but a gray and yellow hammer just looks like a more interesting hammer).
Unity
The icons are all unified in a few different and obvious ways. First, they all use a combination of the same three colors; yellow, gray, and a black stroke. There aren't any other colors added to the set, and they are also all the same shades throughout. Another way they're unified is that they all have the same stroke weight. Combining the stroke weight and use of color leads onto one other way that they are unified, and that is the simplicity of them. Cory actually mentioned in the podcast that it helps to avoid complexity in icons and keep them concise. The creator at queue did a good job in keeping the icons simple, and keeping them all simple. The unity of stroke weight and color all add to this because they are elements that stay consistent throughout.
