The terms 3% and 4% often relate to the percentage of the anchor bolt’s yield strength in relation to the concrete’s compressive strength. For example, a 3% concrete anchor bolt means that the bolt can withstand loads up to 3% of the concrete's yield strength, while a 4% bolt can handle loads up to 4%. This distinction is vital for engineers and contractors, as it influences load calculations, safety factors, and the overall design of the structure.

2. Corrosion Resistance Many hex head bolts come with protective coatings, such as zinc plating or galvanization, which enhance their resistance to corrosion. This feature is particularly important in outdoor or marine environments, where exposure to moisture and harsh conditions can lead to rapid deterioration.