TIGRADE4mm 6mm 8mm 10mm Black Titanium Rings Wedding Band Matte Comfort Fit for Men Women, Black, 6mm, Size 9

Can this ring be engraved?

I got the wrong size how do return it and get the perfect size ?

Is it true to size or do I need to go a size bigger or smaller?

I ordered two. hers 6mm size 6 (16.5mm diameter) was perfect fit. mine (diameter 20mm), selected #11 was 2mm big. which size should i order?