Female to female thread adapter for filters anyone?

I am in search of a 77mm female to female thread adapter for my filters. Imagine a threaded extension basically. You could screw a filter onto both sides of the ring.

Basically I want to screw a filter onto a cokin filter adapter ring. That way I can slip the round filter into the actual filter holder. Instead of using sprocket filters for my polarizer, I could then just use any round filter inside the cokin holder.

Does anyone know where to find something like this?

How does the Canon gelatin filter holder system work. The adapter rings looked like female to female, but I couldn't tell from the online pictures. Otherwise, I haven't been able to find anything readily available.

EDIT: and yes, I know I can just attach my filters backwards for this to work...but some of my filters have no front threads!

I'm not sure what you're trying to achieve that can't be done by screwing the filter onto your lens and the adapter onto the existing front threads of the filter. If you want to put the round filter forward of the adapter (so it is actually within the filter holder), I don't think there's anything that would do what you want; you'd need to tap the front of the adapter to have some threads but you could then directly attach the filter to the adapter. This does assume that the round filter would clear the opening in the Cokin holder. And if you wanted to use a polarizer you'd find it very difficult to turn it with the square filter in the Cokin holder (if, in fact, the round filter cleared the square filter).

I am trying not to buy a second set of filters for my Leica system. If it is just a polarizer, yes I can attach that to the lens, and then attach the filter holder.

However, some filters that I have are in "thin-mount" versions. So I cant mount the filter holder to them, and I cant use them in reverse.

In a cokin P or Z system, a 77mm filter fits just fine with the 77mm filter adapter. As for polarizers, I have no problem turning the filter while it is in. Even if a I have a grad behind it.

I was hoping to be able to just use one set up between my two systems. I just need a way to work with my thin-mount filters. Also, polarizers do not quite work the same in reverse.