Print these out in at least 20% infill. I used an M5 x 15 mm Grub Screw and wing nut. Push the screw head onto the key, it may be very tight, and then push into the bottom part so that it is flat with the surface. Cut a 1/4 sheet of sandpaper and wrap around the bottom part. Place the top part on so that the sandpaper is sandwiched into the groove.You may want to add a washer and then put on the wing nut to hold things together.