Featuring an aluminum frame with small built-in magnets, the Mist Diffusion 1/4 + 3-Stop ND Magnetic Clip-In Filter for Sony E from Kolari Vision secures magnetically to the camera mount, and your lens then mounts on top. The filter sits securely between the camera and the lens. It's compatible with full frame Sony E-mount cameras. The filter material is glass. A small removal tool is included but not required. The compact tool looks like a guitar pick and is included just in case, as the filter can easily be removed by hand.
Compatibility
Sony E-mount full frame cameras, including the a7, a7 II, a7 III, a7S, a7S II, a7S III, a7R, a7R II, a7R III, a7R IV, a9, and a9 II