Print with some strong settings.  I printed this with 3 perimeters, 50% infill, PETG, 0.6 nozzle. I printed it on its side (as seen in the picture and also add some supports to help keep it on the bed). When I used it, the plastic bent a little but the shape recovered after use. 

I have included the Fusion file so you can modify it for your nut & bolt.

Additional Parts: M8 Nut+Bolt

When using it, I suggest putting the nut that holds the wiper arm on so its flush with the top of the bolt. That way the bolt on the puller has more surface area to stay in contact with.