This section is from the "Architectural Iron And Steel, And Its Application In The Construction Of Buildings" book, by WM. H. Birkmire.. Also see Amazon: Architectural Iron And Steel, And Its Application In The Construction Of Buildings.
Hexagon-Head Bolts are needed where the conditions will not allow of the turning of the square nut, especially when the flanges of column connections are small and holes in knees of beam connections are close; they are also used for surfaces where the square-head bolts are an objection to the finish of the work.
Button-Head Or Carriage Bolts are principally adapted to bolting wooden treads to wrought-iron strings; the circular or flat head making a smooth surface on top of tread, and the square portion of bolt giving a shoulder for tightening the nut.
Countersunk-Head Bolts are used for all work re-quiring a smooth surface.
Screw-Head Bolts are employed for a similar purpose, the slot in head being afterwards filled with putty and painted.
Tap Bolts are required for all connections where it is impossible to get a nut on the end. The hole to receive this bolt requires to be tapped, that is, a thread cut in the drilled hole where the bolt is to be screwed.
These are for heavy work, to make a finished surface, and where screw-head bolts are too light. The square end can be taken hold of by the wrench and tightened up, and the end projecting then cut off.
Double And Single Expansion Bolts are for fastening all manner of work to smooth surfaces. All that is required to secure them is a hole of sufficient size and depth, from one to four inches, to insert the bolt expansion; then by-turning the head, as with a common bolt, the expansions are drawn toward each other, thus causing them to bind in the strongest manner. These bolts have an advantage over other fastenings in that they can be removed with ease without injuring the surface of the work to which the bolt is fastened.
The double expansion is used where great strength is required, and is made in all sizes and lengths.
Lag Screws are used in the same manner as expansion bolts, but a plug of metal or wood is required to be driven in the hole before inserting the screw.
To get the full value of the diameter of a tie rod or bolt, the ends on which the nut is screwed are heated and forged thicker; the thread is then cut on the increased diameter.
Open-Drop Forged Turn-Buckles, Pipe Swivel And Arm Swivel are used for tie bars in trusses, etc., with a right and left thread cut in each open end to draw together or extend the length of tie.