Online Parts Store › Phillips Machine Screw - Flat Head, 5/16"-18 x 1-1/2" Image 1 of 1 Phillips Machine Screw - Flat Head, 5/16"-18 x 1-1/2" $30.99 18-8 Stainless Steel. Add To Cart Added! 18-8 Stainless Steel. You Might Also Like Seachoice 01531 Hex Nut, 3/8-16 $30.68 Flat Washer, 7/16", .062" Thick, OD 1-1/8" $27.80 Stainless External Tooth Lock Washer #10 $14.42 308 Piece Stainless Steel Fastener Display $6,664.43 Phillips Tapping Screw - Truss Head #10 x 3/4" $31.18