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Galvanized steel roof curb adapter, square frame, 21 in curb side to 18 1/2 in fan side

Dayton

Dayton 3AZK8 Roof Curb Adapter 18-1/2 to 21 in

SKU CH-8BPT-ZT363 MPN 3AZK8

Adapts an 18 1/2 in fan base to a 21 in roof curb, includes fasteners and galvanized steel construction

  • TypeDrain Components
  • Adapts 18 1/2 in fan base to 21 in roof curb
  • Galvanized steel construction resists corrosion in rooftop environments
  • Includes eight 1/4-20 Tinnerman speed nuts and bolts for secure mounting
  • 5 in overall height with 2 1/2 in top flange ensures proper fit
  • Designed for downblast, filtered supply and upblast fan types

Roof Curb Adapter 18-1/2 to 21 In

The Dayton 3AZK8 is a galvanised steel roof curb adapter designed to connect a fan base measuring 18-1/2 inches square to a 21-inch square roof curb. It functions as an increaser for downblast, upblast and filtered supply fans. The assembly includes eight 1/4-20 Tinnerman speed nuts and eight matching bolts for secure fastening.

Adapts 19 In Fan Base to 21 In Curb

This component replaces the need for custom fabricated transition pieces when installing a fan with a 19-inch base onto an existing 21-inch roof curb. The jump is justified when the curb opening is fixed and the fan base is smaller, eliminating gaps that would otherwise compromise weather sealing and structural attachment.

Suits HVAC Installers Retrofitting Fan Bases

The adapter suits contractors adapting smaller fan bases to larger curb openings in commercial ventilation systems. It is not intended for installations where the fan base matches the curb size exactly, nor for applications requiring a reducer rather than an increaser. Builders needing different dimensional transitions should verify compatibility before ordering.

Highlights

  • Adapts 18 1/2 in fan base to 21 in roof curb
  • Galvanized steel construction resists corrosion in rooftop environments
  • Includes eight 1/4-20 Tinnerman speed nuts and bolts for secure mounting
  • 5 in overall height with 2 1/2 in top flange ensures proper fit
  • Designed for downblast, filtered supply and upblast fan types

Specifications

TypeDrain Components
BrandDayton
Model3AZK8

Questions about this item

Will the 21 in curb-side flange align with my existing roof curb bolt pattern?

The adapter flange is 21 in square outside dimension with two fasteners per side, designed to match a standard 21 in roof curb.

Which fasteners go on the fan base and which on the curb during installation?

Use the eight 1/4-20 x 3/4 bolts with the included Tinnerman speed nuts; bolts pass through the adapter into the fan base, speed nuts secure the adapter to the curb.

Will the galvanized coating on the 18 ga steel need re-treatment after a few years?

The galvanized finish is intended for the service life of the adapter; no scheduled re-coating is required under normal conditions.

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