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 Screw - Pan Head, #8 x 5/8" $18.01 Carriage Bolt, 1/2"-13 x 4" $109.86 Stainless Countersunk Finishing Washer, #8 $14.36 Flat Washer, 5/16", .062" Thick, OD 7/8" $21.67 Phillips Tapping Screws - Flat Head, #4 x 1" $14.93