Fig. 131.
71. Screws.
—Screws, like nails, are made entirely by machinery. They are packed in pasteboard boxes and sold by the gross. The size of a screw is designated by the length in inches and the size of the wire from which it is made; thus, 1 inch No. 10 flat-head bright screw.
The gage of wire for nails and the gage of wire for screws should not be confused. [Fig. 132] is a full-sized illustration of the gage used for determining the size of wire for nails. The numbers apply to the openings at the edge, not to the circular parts. The notch at No. 1 will just slip over No. 1 wire. [Fig. 135] is a full-sized illustration of a wire gage for screws. The gage is slipped over the screw just below the head.
Fig. 132.
Flathead screws are used for ordinary work. Roundhead screws are used because they are more ornamental. [Fig. 133]. Either kind may be made of steel or brass. Steel screws are often blued by treating them with heat or an acid.
