M86x1 filter holder for LOMO square front anamorphic lens or attachment

For sale is adapter (holder) to mount M86x1 round diopter or filter in front of LOMO square front anamorphic lenses or attachments (50mm, 75mm, 80mm).

Square opening is 83x81 mm. Fits round diopters and filters with M86x1 thread and matte boxes with 95mm opening.