From my little experience with playing around with the Kick/Fuse/Blast some tools are the same, some are not. The screwdrivers and scissors are all interchangeable AFAIK, but the long tools like the blades, saws and files aren't quite a direct swap. The 'kick' on the tools are larger on the Fuse/Blast then on the Kick (confused yet?

)
OK the 'kick' on a blade is this bit highlighted with the red arrow:

What it does is rest on the bottom of the backspring (or multitool handle in this case) and sets how deep the blade will sit into the tool. As the 'kick' on the Fuse/Blast tools are larger then it means that the end of the blades stick up out of the handles when they're installed on a Kick. So to make them fit on you have to file them down to size.
Not sure how relevant this is to your mod, but I hope it helps.