Having printed up three of those handles for Show-n-Tell, I preemptively installed one in the hasn’t-failed-yet clamp, and poked the support out of another to show how it works. They’re just the cutest little buttons:
The fins are a touch under 4.5 mm end-to-end and 1 mm (2 × 0.5 mm) across, with layer thickness = 0.25 mm. The first layer fill looks a bit lackadaisical, but the bottom of the surrounding handle came out glass-solid with barely visible joints between the threads, so the settings work fine for larger objects.
The tip of each fin has a scar where the overlying perimeter thread bonded to it. Skeinforge is set to extrude the perimeter first, which would squirt that circle (well, pentagon) into mid-air… which is why this support plug lies in wait below.