DISCLAIMER - I'm not suggesting this info is 100% accurate but it might prove valuable to someone in the future?!?! As always you should contact Benelli Customer Service to get the final word.
Found this at Brownell's site;
Q: Benelli choke tube systems.
A: There are three known choke tube systems that have been used on Benelli shotguns commonly encountered in North America. They are as follows:
First Generation: External Thread System. This is the earliest of Benelli choke tube systems and is typically found on the SL-80 Series: Models 121 and 123, from 1960 through 1986. The thread is on the outside of the barrel and the choke tube has a female thread. These chokes are very much like the old Weaver choke tube system. This requires a special spanner to remove and install the tubes. No current source for these is known at this time.
Q: Franchi/Benelli choke tubes interchangeability.
A: Franchi was purchased by Beretta in late 1997/early 1998 and has come under the Benelli U.S.A. division of Beretta.
There has been some confusion about pre and post Beretta/Franchi choke tube applications. Benelli U.S.A. is telling dealers and consumers that the Benelli/Beretta thread pattern choke tubes will fit the Franchi shotguns. This pertains only to Franchi shotguns marked Imported by Benelli USA.
Franchi shotguns that were formerly imported by American Arms and made prior to the Beretta take over of Franchi will not use Beretta x .75 Metric pitch top thread tubes. Currently, Colonial Arms has these thread patterns available.
Second Generation: Internal Thread System. This system was used on models imported by Heckler & Koch U.S.A. from 1986 through 1995. The barrel is internally threaded with a male thread on the choke tube. The threads are square and are located on the muzzle end of the tube. The major diameter of the threads is .810". The tube has a nominal overall length of 1.888". Included in the overall length is a collar with a nominal length of .118". (1.77" length from face of barrel muzzle to breech end skirt of the tube) This collar extends from the muzzle of the barrel and uses slots for the tube wrench.
Third Generation: Internal Thread System 1995 to present. This barrel is internally threaded with a male thread on the choke tube. The threads are square and are located on the muzzle end of the tube. The major diameter of the threads is .810". The tube has a nominal overall length of 2.050" from the face of muzzle to the breech end skirt of the tube. This system is interchangeable with the Beretta Mobil Choke style choke tube system.