Step bolts have a lower profile head than carriage bolts. The square neck under the head locks the bolt into place.DIMENSIONAL ATTRIBUTES Diameter (Nominal): 3/8" Thread Pitch: 16 Diameter (Dimension): 0.375" Diameter (Minimum): 0.36" Diameter (Maximum): 0.388" Length (Nominal): 2" Thread Length (Nominal): 1" Neck Width: 0.388" Neck Height: 0.219" Head Diameter (Minimum): 1.188" Head Diameter (Maximum): 1.219" Head Height, Overall (Minimum): 0.188" Head Height, Overall (Maximum): 0.208"PRODUCT ATTRIBUTES Category: Step Bolts System of Measurement: Inch Brand: Aspen Fasteners Head Style: Truss Head Head Style Detail: Square Neck Thread Length: Standard Thread Length Thread Direction: Right-Hand Thread Material: Steel Material Grade: Low Carbon Steel Coating: Zinc Plated Coating Color: Clear Origin: Origin Undefined Standards and Specifications: ASME B18.5