The slots are for the insertion of a cotter pin to secure the nut when used with a drilled shank fastener

3/16 x 2 Powers Round Toggle Bolt Zinc Plated (50)

1 5/32 x 6 Reduced Shank Drill Bit (1/2 Shank)

With traditional toggle bolts

3/4-10 Cap Nut Nickel

63/64 x 6 Reduced Shank Drill Bit (1/2 Shank) Nylon Insert Locknuts Zinc Plated The slots are for the63 64 x 6 Reduced Shank Drill Bit (1 2 Shank) . Expands the size range capacity of a 1 2 inch portable drill chuck. Common flute and overall length for minimal adjustment during tool changes. Precision ground for high degree of concentricity between shank and body diameter. Ideal for drilling in low and medium tensile strength materials.