so says their website:

For Use With

Dayton Roof Mounted Centrifugal Upblast and Downblast Ventilators Having a 17 to 30 in Square Base

compatible with:

1MBE6; 1MBE7; 1MBE8; 1MBE9; 1MBF1; 1MBF2; 2RB65; 2RB66; 3GY66; 3GY67; 3GY70; 3GY71; 4HZ32; 4HZ33; 4HZ36; 4HZ37; 4HZ40; 4HZ41; 4HZ44; 4HZ45; 4HZ48; 4HZ49; 4HZ52; 4HZ53; 4HZ56; 4HZ57; 4YC64; 4YC65; 4YC66; 4YC67; 4YC68; 4YC69; 4YC70; 4YC71; 4YC72; 4YC73; 4YC76; 4YC77; 4YU88; 4YU92; 4YU93; 4YU94; 4YU95; 4YU96; 4YU97; 4YU98; 4YY13; 4YY14; 4YY15; 4YY16; 4YY17; 4YY18; 4YY19; 4YY75; 5PV06; 5PV07; 5PV08