The Mossberg 20 gauge Silver O/U use the Huglu choke tube pattern. So any of these Trulock Precision Hunter Huglu 20 Gauge Shotgun Choke Tubes should work with that shotgun.
Trulock and Carlson INCORRECTLY recommend Huglu choke tubes for the 20 gauge Mossberg Silver Reserve. The Huglu tubes barely engage the barrel threads before coming to a cold stop. Get the Beretta Mobil. Trulock customer service sent me a Beretta Mobil choke as a Huglu replacement, and I submit this answer based upon firsthand experience.
The Huglu choke tube will barely engage the Silver Reserve barrel threads and then stop cold. I sent a picture of this phenomenon to Stacie Stallings of Trulock, and she sent me a Beretta tube for the 20 gauge Mossberg Silver Reserve. Trulock and Carlson both incorrectly recommend Huglu for the Silver Reserve...Beretta is the perfect choke! Mossberg does not offer many Pro Factor OEM choices. Good thing we have Trulock options!! Be sure to order the Beretta.