This 4 aperture blade consists of 4 symmetric open spaces and 4 symmetric closed spaces. Hence the "open" time is the same as the "closed" time. The blade is made of sheet aluminum with thickness ranging from 0.025-0.07". The blade is made from an electric discharge machining (EDM) process where a laser cuts the blade pattern onto a thin aluminum sheet. The blade is then anodized black. There are three screws at the center that mount it to the chopper shaft coupler.
 
Technical Specifications:
Blade thickness: 0.025-0.07"
Mount: three screws to chopper motor shaft coupler
Outer blade diameter: 4"
Inner aperture diameter: 3.5"
Inner circle diameter: 1.5"