I have a Century Precision Optics mattbox that accepts a 4" wide drop in filter. The length of the filter tray/folder/sled is not important.There are plenty available on the internet but the prices are insane! If I could find just the filter holder, I could mount one of my polarizers. The filter holder has thumb screws on the left and right sides to allow you to rotate the polarizer. I could also use the standard filter holder and just pull it up to make any adjustments and then drop the holder back in. I have plenty of filter holders but none are 4" wide.

Whatcha got?