When I took Mechanical systems in college, I found identifying grashof types quite difficult, being a visual learner, I thought someone might be able to benefit from getting their hands on a real 4 bar linkage model to see how each grashof type is made; and how this effects the crank, coupler, and rocker. This model has the parts to be able to make all the grashof types and you can determine if they make up a double rocker system, a drag link system, a parallel link system or a simple crank-rocker system. This print is made up of 3 different lengths of links and a pin to be printed multiple times to connect all the links.
I have included a link to Wikipedia about what links make up what grashof type so you can try for yourself. I haven't really seen anything on the market like this so I made it myself. It only was about 18g of filiment which translates to $.36 to make.