This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
As in the case of Fig. 49c and 49d the clearances at one end will be 1/4 inch and at the other end may be more, and should be, in order that the distances l1 and l2 shall be the same. (The distance from the first rivet to the end of the angle is usually 1 1/4 or 1 1/2, generally the latter.) It must not be understood that the clearance is exactly 1/4 inch; it must be at least 1/4 inch, and may be more, up to 3/8 inch or 1/2 inch in order that the distance from the rivet to some other point or rivet may be in an even 1/16 inch or 1/8 inch.
When I-beams or channels are placed as mentioned above, 1/2-inch clearance or more instead of the 1/4-inch is required, one of the most common cases where such clearance is required being shown in Fig. 50. For other clearances in beams see "The Detailing of Beams," page 72.
Wherever bolts, rods, upsets, or rolled bars pass through a hole or slot, the aperture should be 1/8 inch greater in diameter or 1/4 inch greater in dimensions in case there is a slot. The above is in case the material is rolled steel or iron. In case of a casting, 1/4 inch should be added to the dimensions of the member which is to pass through the opening.
Plate I. Stress Sheet of Truss Bridge.
THE HOTEL LASALLE, CHICAGO.