This is a detail from the 12 brothers foundation, a link is listed in the post below. A few thoughts about the press pictured in the portrait of Hans Landaver, dated 1532. Foote identifies this as a small standing press. I think it is a German style press that is lying on it’s side– often these are used to clean spines or tie up when covering. It would make little sense to press a book like this once the bosses and corners were attached- more likely it is holding the book for purposes of illustration. Especially when viewed from this angle, it is uncannily similar to a sewing frame– in fact the edge of the bench almost mimics a top crossbar. This press is puzzling, and I can’t figure out how it would function. I assume the squarish nuts that form the ends of the screws would be used to tighten this press, but the smaller circles on them seem to indicate they don’t move along the thread. Possibly the wood is directly threaded? Maybe they function to keep the threads from pulling through, and both pieces of wood are drilled for clearance, and a nut would be attached from the other side? The thread angle is roughly 45 degrees, which would be unusable, but it is a fairly common artistic convention for the time.
Peachey Conservation 
I think the screws are just badly drawn, sketched in to give an impression of screwness rather than exact realism. Notice the left-hand thread, which seems a common in artists’ portrayals as it is rare in real objects. On the proportions of the press: my impression is that tall finishing presses with the screws near the top edge were popular in Germany and Scandinavia until recent decades. This looks like it has similar proportions, though with fixed screws and loose nuts, and with a top edge that is square rather than rounded over in the more recent manner.