itig the upper or outer end as required. Any plunger subject to much wear must be well hardened or it will soon become useless.
Even if made of drill rod the best method is to case-harden them in cyanide, then polish the wearing end smooth with an Arkansas hone.
In Chapter 5 I have mentioned round Bessemer steel rods as being the best material for MAKING SWIVELS AND LINKS FOR SLING STRAPS. The size rods ordinarily selected for this use is 9/64 inch, and the method of making the swivels and links is as follows: First, rub off the copper coating by drawing the rod back and forth through emery cloth held in the fingers. Next make up the bending form by taking a piece of flat bar cold rolled steel and rounding the edges by grinding or filing. This bar need be no more than six or seven inches long; its width and thickness to be the dimensions desired for swivel or link. A swivel to take the 1 1/4 inch government sling should be I 1/4 inch by 5/16 inch inside— so make the form from this size bar; a 7/8 inch sling calls for swivels and links bent on a 7/8 b/ 5/16 inch bar. Set this bar upright in a strong vise, with one end of the Bessemer rod caught by the vise; then wind the rod around the forming bar in a close spiral until all of it is wound up—see Figure 137. Strike each coil on the flat side with a hammer after bending over the rounded edge. When the entire rod is wound like a spring on the forming bar—or when you have as many coils wound as you expect to need cut the coils down the center of one flat side with a hacksaw, when they will drop off the bar. The coils will be perfectly formed links except that the ends are twisted sideways an amount equal to the diameter of the stock. They may be blued at this stage, or the entire swivel assembly may be blued together. If making links for sling, bring the ends together smoothly by holding the closed side in a vise and bending the ends toward ccnter with straight jaw plier3. Then buff them on the wire buffing wheel, and blue by the heat and oil method described in Chapter 20.
SWIVEL SCREW. The loop or link is only half the swivel; but before going into details of a finished swivel with screw and link permanently joined, we must consider the type of screw necessary for use with detachable swivels. As these swivels (Figure 151C) are just a trifle over 1/2 inch between the side bars, we need a
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