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Grade 9 Yellow Chromate Alloy Steel Hex Bolt, 1/2'-13, 3/4' Length (Pack of 10): Industrial & Scientific. Grade 9 Yellow Chromate Alloy Steel Hex Bolt, 1/2"-13, 3/4" Length (Pack of 10): Industrial & Scientific. Hex bolts have a chamfered point to aid insertion into a tapped hole or nut. Length is measured from under the head.。Grade 9 fasteners (also referred to as Grade L9) are extremely strong and are made of a high-grade alloy steel. They are grade-marked on the head with nine radial lines, a dot, and the characters L9, and have a minimum tensile strength of 80,000 psi. Yellow Zinc Chromate fasteners have been coated with zinc and with yellow chromate. As a result they offer corrosion resistance that is slightly higher than clear zinc.。Hex head fasteners can be driven with simple wrenches, and require minimal clearance above the fastener because they can be driven or loosened from the side. 。A threaded fastener's size name includes information about the major external diameter, followed by the threads per inch, which indicates if it is coarse or fine. Coarse threads are better when working with brittle materials; they are sturdier and are easier to thread and unthread compared to fine. Coarse threading also allows for thicker coatings and platings. 。 。 。