1/4-20 x 5 Six Lobe Flat Floor Board Screw Type F Black Phosphate BPU188 They have a flat head

They have a flat head with an undercut that allows the screw to be countersunk below the surface of the material

These 8-15 x 3/8 Phillips Oval Undercut Self Tapping Screw F/T Type A 18-8 Stainless Steel are designed for use in a variety of applications

#8 Internal Tooth Lock Washer Black Zinc and Bake is a washer designed to prevent loosening of threaded fasteners due to vibration or shock

The nut is also thin

preventing the washer from loosening or coming off

1/4-20 x 5 Six Lobe Flat Floor Board Screw Type F Black Phosphate BPU188 They have a flat head1 4 20 x 5 Six Lobe Flat Floor Board Screw Type F Black Phosphate This screw is designed for use in floor board applications. It has a 1 4 20 thread size and is 5 inches long. The six lobe drive head provides a secure grip for driving, and the flat head sits flush with the surface of the material. The black phosphate finish provides corrosion resistance and a professional appearance.