M4 shroud fitment
 

I'd like to know what I need or need to do to fit this kind of shroud on an ares M4 with this kind of fitment.

http://i3.photobucket.com/albums/y82...pswixzzn8h.jpg

http://i3.photobucket.com/albums/y82...pspwwijbcm.jpg

http://i3.photobucket.com/albums/y82...pssabyanh0.jpg

I need thread on the gun, but there isnt any! what can I do?
thanks

The black part still on the gun needs to go, that can be unscrewed.
Also, that's a RIS.

Only paintballers call anything around the barrel a shroud.

I know the first part comes out. the one with sqare side and hole for bolt. but the black round one stays there?!
I think I found my answer trying to take an other pic. I think I can unscrew the black part too.

haha!!! I was wondering what kind of tool I could use to unscrew that thing with square hole in the end. Decide to use hand and it finally worked :D