This is an extra large grip to turn an M8 screw into a grip screw which you can turn by hand without any tools and apply a lot of force.
I made this as a replacement part for my Pallucco Fortuny lamp (great design but poor engineering). The lamp has two grip screws to fixate the main reflector at an angle, however the massive steel frame is so heavy that it would never stay there and you just couldn't turn the little screw any tighter by hand. This screw is very large, so it can be tightened much easier, and it does the job.
This design consists of two printed parts and it requires one M8 screw with hexagonal head (normed as DIN933) of your prefered length (it needs to be 4mm longer because 4mm of the thread remain inside the screw head). You can also scale the model to fit M6 or other threads (look up the DIN933 specification to calculate the proper scaling factor).
100% for inner part, 25% for outer part
Print the inner part with 5 shells and 100% infill as it needs to withstand a lot of force in both axial and radial direction. The outer part doesn't need to be that sturdy can be printed with default settings.
Put screw into small inner part with thread through hole, apply glue (I used Acrifix), push outer part on top, let dry, done!