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

which allows for a better range of fits to cut down on the potential for stripping

1/2-13 x 2 1/2 Square Head Set Screw Cup Point 18-8 (A2) Stainless Steel

10 x 2 1/2 Simpson Bugle-Head Wood Decking Screws - 6-Lobe Drive 305 SS - Deck Pack (350)

3/8-16 x 1 1/4 Grade 5 Hex Cap Screw Zinc Plated Domestic USA (800)

5/8 x 6 DeWALT Engineered by Powers SCREW-BOLT+™ High Performance Screw Anchor Mechanically Galvanized (25) 5/8 Dowel Pins Alloy Steel The slots are for theThe 5 8 x 6 DeWALT Engineered by Powers SCREW BOLT+ High Performance Screw Anchor Mechanically Galvanized (25) is the perfect anchor solution for heavy duty projects. Constructed of heat treated steel, this anchor is built to last and can support up to 1,500 lbs. of tension and shear force. Galvanization adds protection in demanding environments.