Structural DraftingConnection DetailsBeam GagesSteel fabrication is based on standard measurements called gages to reduce possible errors in matching connections.Horizontal hole spacing is generally 3" apart (center to center) with the first hole located 3" below the top of the beam .Edge distances from centers of holes to edges of angles and beams are found in Table J3.4.Using Table J3.4for minimum edge distances and the standard hole spacing gages, dimensions can be applied to the connection of the angle and beam to begin developing the connection detail drawing.Angle sizes can be determined from the standard hole spacing and the minimum edge Angle GagesThe size of one leg of a connection angle can be found using the minimum edge distances in Table J3.4.Leg of angle = 1/2" + 1-1/4" + 1-1/4" = 3"1Structural DraftingConnection DetailsCenter to Center CalculationsThe center to center distance must be calculated based on the assembly clearances for the assembly of the connection. One method of calculation utilizes the Entering and Tightening Clearance, in. Conventional ASTM A325 and A490 bolts found in Table 7-16.For example, given a connection using a 1/4" thick angle and 3/4 diameter A325 High Strength bolts calculate the center to center distance.C2 = 3/4"H2 = 1-3/8"Angle (t) = 1/4"tw of beam = 5/16"C to C distance = ((C2 + H2 + Angle (t)) x 2) + twC to C distance = ((3/4" + 1-3/8" + 1/4") x 2) + 5/16"C to C distance = 5-1/16"Another method of calculating the center to center distance is based on the tools used in the assembly and the actual sizes of the fastening components. The clearance dimensions are given in the Erection Clearances for Rivets and Threaded Fasteners. For example, given a connection using 1/4" thick angle and 3/4 diameter A325 High Strength bolts calculate the center to center distance.Angle (t) = 1/4"Washer (t) = .177"Nut (t) = 5/8"Bolt Projection = 1/8"Clearance (F) = 1-1/4Total = 2.43"Center to Center distance = (2.43") + tw + (2.43+)Center to Center Distance =