This fan is a 21 CFM fan fitted with Humphrey’s Rigid Adapter. Made to work with the Fireboard drive system.  Easy hook into the drive cable. 

Pair it with the 3/4”, 1-1/2” or 2” Humphrey’s Ball valve fitting for a snug fit making it worry free.

All fittings and adapters made by Humphrey's with highly sophisticated cnc machinery.