Same as the Mossberg500 .Its a kind of "one way "[or star] washer that has about six micro splines that pop up into a recess on the bolt behind the thread thus capturing it.
As such it isn't designed to be removed at all.So it is a piece you have to destroy if you want to change out the captive bolt cap.

I changed mine last year,and if you order a replacement bolt[I'd suggest Uncle Mikes of Oregon.About 20 USD on" Flea bay"] They provide the replacement cap,swivel,and one way washer and tool to seat it as well.Well worth the money,otherwise it is a almost impossible fiddly and fustrating job to try without the proper tool.

http://www.midwayusa.com/product/150493/the-outdoor-connection-total-magazine-cap-with-sling-swivel-stud-mossberg-500-maverick-88-12-16-20-gauge-black

Like this? Says it comes with the special tool.

http://www.cheaperthandirt.com/product/44429

Or this? Call ior email one of these outfits they can probably help. Sometimes YouTube is hit and miss.

I used to own a Model 590, I think there are some vids out there on cap removal, but not sure how good.

http://www.midwayuk.com/

What about this, does that do any good for anyone there?