When it comes to rifles i'm a bit of a novice so I could use some help with the following question's.

1)If a rifle is listed as haveing a threaded barrel does that mean you can add a silencer to it?
2) Does two inches matter interms of barrel length? A rifle i'm looking at buying is out of stock in a 22inch barrel but is in stock with a 20inch barrel. Both are the same caliber and are from the same company (savage arms) To most these are probably simple questions but like I said i'm a bit of a novice when it comes to stuff like this so any help is appreciated. Thanks