New Holland 300 Series Service Manual page 25

Inch Lock Nuts, All Metal (Three optional methods)
Grade Identification
Grade Corner Marking Method (1)
Grade A No Notches
Grade B One Circumferential Notch
Grade C Two Circumferential Notches
INTRODUCTION
4
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Flats Marking Method (2)
No Mark
Letter B
Letter C
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Clock Marking Method (3)
No Marks
Three Marks
Six Marks