From the first person who I heard use the term, a week or so ago. Minor edits have been made, for clarity, and my comments appear within : Now this is the only person I've ever heard tell this story, so am awaiting third-party verification before offering it up as fact. At some point, the practice of affixing a washer to the ParCan's safety screen became obsolete, as the ACL lamp got its own mini-reflector or disc inside the lamp. On a Beam Projector, I have heard the black cylinder and black dot (later a small spherical reflector) referred to as "filament blockers." I have heard the small spherical reflector referred to as a "kickback reflector," prior to them being used in ERSs. See also the thread What is a Bortz dot?.