This print is designed to be used with the DtM-v3.1 face shield to better retain the transparent sheet, mostly when a very thin sheet is used (retroprojection acetate or similar) It should preferably be printed on the same printer as the shield itself (for dimensional compatibility) and the best material is PETG, as it's more elastic than PLA. The wavy shape helps with elasticity.
the best way to put it on is to insert the transparent sheet, insert the 2 sides with the center on the hood, then slip the center into position with the help of the hood angle.