How does the line weight slider work?

When you select "Filter by: line", a slider appears that allows you to adjust the search results based on line thickness. You can choose from faint to bold and block off the slider on either side of the spectrum to find the exact style you're looking for. 

Faint: Moving the slider to the left shows thinner more, delicate lines

Bold: Moving the slider to the right shows thicker more, pronounced lines.