Basic aluminum bleachers consist of aluminum seat planks, footboard and understructure.   Solid and durable, this kind of bleaches can be built to multi-rows seating system
 
 
Seat plank size
H55mm * W240mm * L (optional)
Seat width
450mm 
Footboard
H55mm * W240mm *L(optional), single or double, standard mill finish
Row width
700 mm
Row height
First row 400mm, 200 mm higher row by row
Understructure
Aluminum 6061
Length
2.25m, 2.5m, 3.6m, 4.5m… …or custom length