All of the M4’s I have bought and received as a FFL have come disassembled? The boxes interior is set up for them to come in pieces. You would not want them to be fully assembled. Things like the bolt handle will punch thru the side of the box and do damage when the boxes are smashed in shipment.
Contact Benelli customer service. They may be able to provide (sell) the fine-thread part. Or, contact Midwest. They may have the correct part.
And for future reference, a pipe wrench isn't a proper gunsmithing tool. Just sayin'. ?
Just added the following
-Briley CF 7 rnd mag tube (thks stranger danger for the info on removing the stock mag tube.. I also didn't use any loctite when placing the new briley one in)
-Briley foregrip
-FFT titanium large charging handle
-FFT red anodized mag follower
-Wolff mag spring
-Mesa tact urbino stock
Mods on order n coming soon
-IWC multi light mount
-Benelli collapsible stock