A design secures to parts with a line of hexhead bolts whose

A design secures to parts with a line of hex-head bolts whose heads have a 1/2\" distance across the flats (i.e., take a 1/2-inch wrench). What is the minimum center-to-center spacing of the bolts that will allow them to be tightened with a standard 1/2-inch open-end wrench?

Solution

ASTM A325 bolts are available in diameters from 1/2 to 1-1/2 inch (for diameters greater than 1-1/2, ASTM A449 specifications should be considered) with a minimum tensile strength of 120,000 PSI for diameters one inch and less and 105,000 PSI for sizes over one inch to 1-1/2. They also come in two types. Type 1 is a medium carbon steel and can be galvanized; Type 3 is a weathering steel that offers atmospheric corrosion resistance similar to that of ASTM A242 or A588 steels. Type 3 A325 bolts shall be marked \"A325\" to distinguish them from standard A325 bolts.

ASTM A490 bolts are available in diameters from 1/2 to 1-1/2 inch diameters with a minimum tensile strength of 150,000 PSI for all diameters, and are offered in two types. Type 1 is alloy steel, and Type 3 is weathering steel that offers atmospheric corrosion resistance similar to that of ASTM A242 or A588 steels. Type 3 A490 bolts shall be marked \"A490\".

ASTM A490 bolts should not be galvanized or electroplated. The problem with hot dip galvanizing is that the molten bath of zinc exceeds the fastener\'s tempering temperature and would cause the fastener to anneal in the bath. In addition, a major problem with hot dip galvanizing and electroplating A490 bolts is the potential for hydrogen embrittlement. This scenario may occur when atomic hydrogen is introduced during the pickling process that takes place prior the plating or hot dip galvanizing process.