Size, Pressure & Special Routing · Size, Pressure & Special Routing
Very small 4–6 inch round branch
Small terminal branch
ConnectionSlip-fit
SupportBand/strap
Before you start
- Confirm the exact 4–6 inch diameter, fitting sizes, collar size, route, support, and terminal connection.
- Inspect small fittings and pipe ends for crushing, overcrimping, and screw damage.
- Verify the route does not require flattening the branch to clear structure.
- Use appropriately small fasteners and keep screw intrusion out of the airflow path.
Tools and materials
Correctly sized small round duct and fittings, approved slip or gasketed components, short approved fasteners, sealant, small bands or straps, snips, crimper where required, and level.
Lay it out
- Lay out the shortest clean route.
- Keep bend radius and collar alignment reasonable.
- Plan supports that do not pinch the small diameter.
Set and support it
- Use small bands or broad straps.
- Support the branch near fittings.
- Keep the pipe round while adjusting.
Make the connection
- 1
Check each end for roundness.
- 2
Seat the fitting fully.
- 3
Install only the required fasteners.
- 4
Seal the joint.
- 5
Connect the next fitting without crushing the pipe.
- 6
Set supports and remove sag.
- 7
Inspect inside for screw intrusion.
Check the install
- Full diameter is maintained.
- No sharp screw projects into the airflow.
- The branch has no sag or flattened spot.
- Joints are fully seated and sealed.
- Fittings remain aligned.
Common mistakes
- Flattening the branch to fit.
- Using oversized screws.
- Overcrimping the pipe.
- Leaving the small run unsupported because it feels light.
Stop and ask
Stop if the branch must be flattened, overcrimped, or forced through a route that does not preserve the full diameter.