My mistake, they are even earlier. They are listed as late Hallstatt, from the Hallstatt D3 period which is just before the La tene era. So circa 500-450 BC.
They are simply called Hallstatt era
Crossbow fibula with foot knob (Armbrustfibeln mit Fusszier).
From what I can tell yours is Mansfeld
Type F3 (based on the knob configuration).
This is from figure 77, page 27(437) of Fibel und Fibeltracht,
part of the Reallexikon der Germanischen Altertumskunde (2000), de Gruyter,
Berlin.
Shawn