The model 150 is our standard multi-cone round ceiling diffuser for either residential or light commercial applications. Outer ring mounts flush to ceiling. Step-down diffuser rings deflect air pattern 360 degrees. This model has screwholes to mount directly to the ceiling. Steel construction, white finish. Note duct ring with damper (Model 155B) is also available for use with Model 150 - this unit combines a T-handle operated damper wita duct mounting ring. If you require the mounting h ring only, no damper, you can order model 156R. Be sure to order by your duct/hole size, not the overall size of your existing diffuser!