M Fixt
Non-ceiling mechanical fixtures, such as floor registers. Shows in mechanical plan, or in the floor plan if you don't have a mechanical plan and you want to show the registers. (We did this on Stevens.)
M Fixt Clg2
Ceiling mechanical fixtures, such as ceiling registers or returns. Shows in mechanical plan and reflected ceiling plan.
M Equip
Mechanical equipment, such as furnaces, air handlers, water heaters. Shows in mechanical plan, electrical plan, floor plan, and section. If you don't want a particular element to show in section, turn the 3D off in the object.