This face shield was remixed from the popular Verkstan model and from DtM-v3.1 (itself a remix of the Prusa RC3).  This was designed in response to a request from a nurse friend who liked the Verkstan for not needing a strap, but the DtM for the shield.  The Verkstan tension band was widened just a little to accommodate larger head sizes, and the DtM sheild was shortened because it's located closer to the face than in the Prusa/DtM models.  I also changed the Verkstan cross-section to give it a little more lateral bending strength.  My experiene was that the original was a little fragile when printed in PLA.  Similarly, the DtM visor was thickened a little, again because I print in PLA.  Finally, the three-hole punch design was chosen to better accommodate the increasing use of report covers and page protectors.  The tabs have an outter diameter that's larger to prevent these makeshift face shield materials from slipping off.