#No!Filter_95mm_110mm_114mm

When camera assistants take their mattebox off a camera but want to leave filters in, they generally put bright coloured tape across the rear opening. This is designed to plug the back of the mattebox, giving you full protection.  It works for matteboxes that have a 95mm, 110mm, 114mm clamp. The interior profile is a nod to the 'no' symbol, which also works as a pinch point to install and remove the plug.