Indeed! As a zip drive is inserted, that arm gets pushed back and reaches a position in the rear where it opens the sliding metal shutter on the zip media so that the read/write head assembly can access the zip disk!
At about the 9:30 position of the drive arbor that three segment arm needs to have a post of some kind into the deck to pivot upon, and just to the left of the pivot a tab for the spring to engage that pivots the arm clockwise until it reaches a travel stop at the front edge of a semicircular track where it waits for media insertion.
The spring assures that the arm is forwards enough to engage the right hand edge of the shutter. If the arm is full back when media is inserted, the arm will not catch the shutter to open it to the left, rather it will just rest on the rearwards face of the shutter.
The arm right end should indeed be muscled carefully into that semicircular track slot.