Ayp OEM Replacement Blade 340-157 
FITS MODELS: 20'' walk behinds 
Mulching blade
length 20'' (508mm) 
Centre Hole 5/8'' (15.9mm)
Outer Holes 3/8mm (9.5mm)
Centre 1 7/8'' (47.6mm)
Width 2 1/4'' (57.2mm)
Thickness .134'' (3.4mm)