Summary This is a fairly thick ZMR 250 spacer designed to be used as a unibody, with all components between the two bottom plates of the ZMR. In addition to fattening the spacer from 10 to 15mms, I shortened the arm mounts from four holes to two holes, which I think is a massive improvement. Here is a list of reasons why: More interior space for components Less weight Less print time Arms can be bolted directly to bottom frame in the inner two holes, increasing rigidity and further decreasing weight from long bolts. Also, the little backstop fits over your spacers and can be used to prevent your battery sliding into your FPV pod in a crash. If your build is like mine, anyway.