Standard size for cameras - 1/4 x 20
Euro standard - 3/8 x 16
US mic standard - 5/8 x 27
I'm not familiar with the A20 so can't tell you what is has but I will recommend that next time you order something from B&H or a similar retailer you add a few of each adapter to your order and keep them in your bag. Never know when you, or a clamper, might need one.