This fits the FX model as well as older models with bay III filter mount.
This is a locking swivel filter attachment that mounts to the camera body and accepts any E46 screw mount filter. It works with both earlier and current Rolleiflex cameras that have a size IV bayonet mount. This adapter allows photographers to swing the filter to the taking lens for composition and a view of the filter effect and then the filter can be quickly swung back down over the taking lens for the shot. This is particularly useful with a polarizing filter but also with black and white photography filters. The filter adapter allows the use of the larger variety of filters that are available in standard threaded mounts and often at lower cost than Bay III filters. While the metal Rolleiflex bay III shades will not fit directly onto threaded filters, an aftermarket screw in hood can be used mounted to the filter
Note: Picture shown with polarizer is the bay IV filter adapter but the bay III is very similar.