Carlson's Choke Tubes Benelli Nova/SN Ber Extrema/1301 CZ 712/912 Magazine Extension 10 Shot Black. These magazine extensions are constructed of blued solid steel and come with spring base clamp with swivel stud (included) to work with quick detachable swivel (not included) and a high visibility follower. The threaded tube replaces you magazine cap and gives you the ability to add extra rounds to you magazine. Easy to follow instructions are included. The magazine extension tube is great for home protection competition shooting and law enforcement. See chart below for the make/model and the magazine capacity. Overall Length of Extensions: 04500 (8.25-inch) 04501 (10.5-inch) 04502 (6.25-inch) 04503 (6.375-inch) 04504 (14.25-inch) 04505 (8.25-inch) 04506 (6.25-inch) 04507 (8.25-inch) 04508 (5-inch) 04510 (13.88) and 04511 (8.5-inch) 04512 (8.38-inch) 04513 (8.13-inch) 04514 (14.13-inch) 04515 (8.13-inch) 04516 (14.13-inch) 04517 (8.5-inch) 04518 (14.25-inch) Magazine round count is for the total capacity using 2 3/4-inch shells including 1 in the chamber when using 3" shells you lose 1 shell capacity. When using 3 1/2" shells you lose 2 shell capacity. Example: 8 shot extension= is 7 (2.75" shells) in the extension and 1 in the chamber 6 (3" shells) in the extension and 1 in the chamber or 5 (3 1/2" shells) in the extension and one in the chamber. Remington extensions require removal of tabs / detent in magazine tube on newer model shotguns All extensions are 12 gauge only. Specifications for Carlson's Choke Tubes Benelli Nova/SN Ber Extrema/1301 CZ 712/912 Magazine Extension 10 Shot: Manufacturer: Carlson's Choke Tubes Color: Black Magazine Capacity: 10 Round Condition: New Country of Origin: USA Features of Carlson's Choke Tubes Benelli Nova/SN Ber Extrema/1301 CZ 712/912 Magazine Extension 10 Shot: Benelli Nova/SN Ber Extrema/1301 CZ 712/912 Magazine Extension 10 Shot Package Contents: Carlson's Choke Tubes Benelli Nova/SN Ber Extrema/1301 CZ 712/912 Magazine Extension 10 Shot barrel clamp plus & spring Carlson's Choke Tubes 04510: Benelli Nova/SN Ber Extrema/1301 CZ 712/912 Magazine Extension 10 Shot Black