Flange bolts feature a built in washer under the bolt head that helps to distribute the clamping load over a larger area.
Serrated Flange Bolts 3/8in-16 X 1-1/4in Zinc Plated Case Hard Steel 25PK The serrations under the flange bite into the surface and help to resist loosening due to vibration..Size: 3/8 inch-16 X 1-1/4 inchHex bolt with a serrated circular flange under the headFlange eliminates need for separate washerSerrations bite into surface and can help to prevent looseningDesigned for use with a nut (not included) or a threaded hole of the same diameter and thread sizeThread Type: Coarse, Thread Class: UNC-2A, Point Style: BluntSpecification(s) Met: ASME B18.1, ASME B18.