Of the two choke tubes that you have pictured, the one on the right (with the groove going around it) looks like all of the flush mount choke tubes I have in my range box... When you have the one on the right installed, do you gave the gap at the bottom???
Give Maverick a call and tell them that the two choke tubes don't match and that you need them to send you a replacement one... they shouldn't have a problem sending you a spare....
Their contact info is:
Maverick Arms, Inc.
Product Service Center
1001 Industrial Blvd.
Eagle Pass Industrial Park
Eagle Pass, TX 78853
PH: (830) 773-9007
Good Luck and let us know how you make out.....
Smitty