A 12-inch stick-on collar is a circular duct fitting used to connect a round duct (often flexible duct or rigid spiral duct) to a flat surface such as a plenum wall, ductboard, sheet-metal trunk, or other duct surface. It “sticks on” to the surface, often via flanges, tabs, adhesive, or mechanical fasteners, forming a transition point (“take-off”) from the flat surface to a round duct run.

Common uses:

To create a “tap” on a ductboard or plenum for a branch run

To connect flexible duct to a flat plenum or trunk wall

As a starting point for new duct runs

Often used behind registers or grilles, or within duct cabinets

These collars may include additional features like a built-in damper (for flow regulation), adhesive or gasket sealing surfaces, or tabs for easier mounting.