@e_stern pointed out that this is the plastic part needed if you get a different barrel for your 1301 Tac and want to swap them easily:
Beretta 1301 Tac Forend Bushing Spacer
Code: C5F172
https://www.midwestgunworks.com/bere...g-spacers.html
(Neither Brownells nor Beretta list it on their respective sites.)
For example, if you want to get the JB400SD28 ribbed barrel and do some more traditional shotgun stuff with your Tac.
Just realized MGW also has replacement C59948 mag tubes. From all the reading I've done on the Tac, that's the one thing that may show signs of wear and lead someone to want to replace it after 3000-4000 rounds. Brownells also lists it, but it's on backorder status. Last time I looked, a few years ago, I couldn't find them listed on any US site; only some random Euro site.