18" Start Collar Galvanized Sheet Metal.
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18" Start Collar Galvanized Sheet Metal 30 gauge K.D. material (Knock Down-open) For ease of cutting and fitting to your ductwork. After closing the seam, the collar is permanently locked. One end is crimped for attachment to ductwork, the other end is dove-tailed for attachment to plenum or register boxes. Sizes are 4" to 20" diameter.