Online Parts Store › Phillips Machine Screw - Flat Head, 5/16"-18 x 2-1/2" Image 1 of 1 Phillips Machine Screw - Flat Head, 5/16"-18 x 2-1/2" $16.00 18-8 Stainless Steel. Add To Cart Added! 18-8 Stainless Steel. You Might Also Like Phillips Tapping Screws - Oval Head, #12 x 2-1/2" $39.93 Flat Washer, #10, .050" Thick, OD 9/16 $16.12 Phillips Tapping Screws - Oval Head, #12 x 1-1/4" $22.30 Nylon Insert Locknut - Stainless 5/16-18 $18.01 Phillips Tapping Screw - Pan Head, #10 x 1" $29.03