Each Self-Adhesive Filter Gasket in this 3-pack from Formatt Hitech is designed for use with a glass or resin 100 x 100mm Formatt Hitech filter while it is placed in a Formatt Hitech 100mm Aluminum Filter Holder.
When installed on a compatible filter, a Formatt Hitech filter gasket can prevent stray light, which could have unwanted effects on exposure, from coming in between an installed filter and a connected lens. These gaskets are designed to be positioned on the side of the filter that directly faces the lens while they each form a seal between the plastic filter slots.