Wouter-
The strut projecting out the rear of the uppermost mast base (the Flyer base) is the rotation limiter arm- The "stock" Flyer setup has a grommet in the middle of the tramp through which the rotation limiter line projects and then it runs through a small block shackled to the rear of the this arm. My original setup had twin small SS tubes bolted to the aluminum mast base and projecting rearward. These are notorious for breaking at the mast base since they have very little vertical support so they get flexed vertically and end up breaking.
These bases look quite nice but I'm interested to see how much heavier they are than my current aluminum bases. Not an issue on my Flyer since it's got ~10 lbs. of lead in it now to get to legal weight!

Kirt