Hoppe dust cap for sidelite strike.  Installed under strike to line the hole in the jamb

Length: 1-5/8" (base) 1-3/4" overall (45.5mm)
Width: 9/16" (base) (16.5mm)
Depth: 9/16"

Related Parts:
Sidelite Thumbturn: 3321300
Stainless Steel Strike Plate: 3317644
Dust Cap for Strike Plate: 3396750
Screws for Strike Plate: Hoppe 2045931 (AADW 2045000-SN)