Husqvarna OEM Replacement Blade 310-078
Requires 3 for 61'' deck; notched air-lift blade 
Length 21'' (533.4mm)
Centre Hole 5/8'' (15.9mm)
Outer Hole 1/4'' (6.4mm)
Centre 1 5/8'' (41.3mm)
Width 2 1/2'' (63.5mm)
Thickness .250'' (6.4mm)