Red dot magnifier question

Hey guys,

I’m new here and need some advice. I just bought my first AR, and I mounted a TruGlo Tru-Tec 20mm red dot on it. I’d like to add a magnifier behind it, but it seems they’re all 30mm tubes. Did I mess up getting the 20mm? Does it matter? Will a 30mm? Any help would be appreciated.

20mm on the RDS is the objective size. 30mm on the magnifier is the tube size (OD). If the center height of both on their mounts is the same you are OK.

Awesome. Thank you.