Master Flow 12 in. x 2-1/4 in. to 6 in. 90-Degree Register Box 90RB12X2.2X6 - The Home Depot
Ceiling/Basement Register Boot - DuctWorks
Amazon.com - Toe Ductor Base Board Vent Under Cabinet Toe Kick Ducting Kit (Important! Please Check The Location of Venting Boot/Hole in Your Home to Make Sure You Need This Version) -
12X2X6-TOEKICK TOE KICK BOOT 2X12X6 | Mid-State Supply
transitioning from 6" round to toe kick - Inspecting HVAC Systems - InterNACHI®️ Forum
Master Flow 12 in. x 2-1/4 in. to 6 in. 90-Degree Register Box 90RB12X2.2X6 - The Home Depot
2″ x 12″ x 6″ Toe Kick Boot – Monroe Equipment
DIY Help - Vinje's Sheet Metal & DIY Heating
Toe Ductor, Floor Vent Under Cabinet Toe Kick Ducting Kit - Storage Cabinets - Amazon.com