This is a replacement forearm for a Rescue Hero figure (circa 2001). Poor Jack Hammer finally had one rescue too many this past week.... 3 year olds have a way of finding the weaknesses in old toys.
I designed this in Solidworks. It took a couple tries to get it to fit and move properly.
It is a TIGHT fit intentionally. I had to sand the bits to fit snugly. I designed this to not need glue, but to also be upgrade-able. I have a work-in-progress hand replacement with interchangeable tools in the works.
Test your fits well before full assembly. I cracked one of the prototypes by forcing the slot/tab together.