Honda OEM Replacement Blade 305-0729
Mulching blade 
Length 18 1/10'' (460mm)
Centre Hole 3/4'' (18.5mm)
Outer Hole 11/32'' (8.75mm)
Centre 2 9/16'' (65mm)
Width 2 3/8'' (55mm)
Thickness 1/8'' (3mm)