Hoop Height / Hoop Thickness 

Allied embroidery hoops are either "Single Height" (designated by SH in the hoop item number) or "Double Height" (designated by DH).  This refers to the thickness (height) of the hoop.
Examples: AWH-320100-SH-abc-000 (Single Height Hoop)
                    AWH-320100-DH-abc-000 (Double Height Hoop)
Single Height hoops measure approximately 1/2" thick.  This is the ideal choice for thinner fabrics such as t-shirts & golf shirts.
Double Height hoops measure approximately 3/4" thick.  The extra thickness provides additional gripping surface area compared to "Single Height" hoops and therefore is the ideal choice for thicker fabrics and also slippery fabrics such as satins and silks.
All Allied Grid-Lock™ Plastic Embroidery Hoops are Double Height.