This Easy 1-2-3 aluminum Stage 2 fan shroud integrates perfectly with your Stage 1 Radiator with 21" wide core. Simply bolt the four corners to the threaded holes in the radiator, and now you've got a nice clean looking radiator system that utilizes the Four-Corner design. The shroud also includes pre-threaded holes for PROFORM electric fans, and mounting hardware to attach the shroud to the radiator. Please Note: This shroud is not compatible with other radiators, because it is designed to integrate directly to PROFORM Stage 1 Radiators. PROFORM Stage 3 Fans will mount directly to the pre-threaded holes, but you can make your own holes and mount any brand fan if that is your preference.