It's a 3 piece servo arm, as you can use two different splines. I originally didn't use enough glue and it came apart on the first turn. Looking at the design, I don't see how it can assemble without glue, as the centre splined section is the only piece the screw goes through to locate the arm on the servo.
I put it together and ran it for about 10 minutes, then my friend ran it into a gutter and broke the left steering knuckle. Oh well, I'll fix it tonight. Other than that, I'm pretty impressed with it!