Can't say for sure. With the Mac The Knife slipper basket installed, the outer slipper backing plate comes up right near where the first shoulder is machined at the end of the threads. With no spur, you can move it at least 0.250" past that.

My claim to fame used to be getting Losi kits where at least one of axles were mismachined (no holes, or no threads), maybe you just got a bum one.