These are Benelli chokes if you have the mossberg barrel. I have had good operation with Trulock chokes. I had my 20 inch tactical barrel threaded by a shop but they could only do a winchester thread.
I am using the extended chokes to give me an extra inch and they pattern very even.
http://www.trulockchokes.com/get-chokes.php?manufacturers_id=16&guage=20&seechokes=See Chokes Give them a call first. they are very helpful. Some models you can find cheaper on Amazon.
Trulock chokes PPB20620
Cylinder 0.000 $26.99 Flush