This is a Sinar 5.5 inch lensboard with Copal 0 sized hole.
Additionally, it has a Calumet Xenophon Gel filter holder mounted to the back with screws. This allows mounting filters in back of the lens. The holder takes 4" filters. The filter holder can be adjusted up to 4cm from the board, to provide clearance to the back of the lens.
In good working condition.
$38 including US postage, $45 including international postage. Paypal accepted.