Fig. 69.—Steel Sharps, screw.
At the time of fitting the shoes, holes are made by first punching a round hole through the heels—and through the toe if desired—then the hole is 'tapped' and a thread formed to fit it in the shank of the sharp which is to fill it. If the sharps are not immediately wanted the holes may be filled with corks to keep out the grit and dirt. When corks are used the wear of the shoe causes a burr to form round the edge of the hole, and before the sharp can be screwed in a "tap" must be worked into each hole to clear the thread. One great objection to this method is that as the shoe wears it becomes thinner, and if much worn the shank of the "sharp" may be too long, and when screwed home cause pressure upon the hoof and consequent lameness. To guard against this steel "blanks" are used to preserve the holes, and when a frost comes they are removed and the "sharps" put in.
The blanks vary in height and of course those least in height are best for the horse's action, but they must not be allowed to get so worn that it is impossible to remove them. These blanks are shown below.
Fig. 70.—Blanks, screwed.
Fig. 71.—Steel Sharps and Blank, Plug shanks.
The "tapping" and "screwing" of shoes is expensive, and in small shops must be done by hand. In large shops a gas engine and a machine would reduce the cost very greatly, and if the system came into general use this method of providing against frost-bound roads could be carried out at much less cost than now. With a view to economy and simplicity a sharp has been invented which requires no screw. The shank may be either round or square. A hole is punched in the heel of the shoe and carefully gauged to the size of the shank of the "sharp." The sharp is then put in and a tap of the hammer secures it. The difficulty is to get the hole in the shoe and the shank of the sharp of corresponding form and size. When this is done the sharp keeps its place and is not difficult to remove. Too often, however, they are not uniform, and then the sharp falls out or sometimes cannot be removed. When the holes are drilled instead of punched the fit is more exact, but this only applies to those with a round shank. A slight taper is given both to the hole and the shank of the "sharp." As with the screw sharps so with these, blanks are used to keep the holes open until the road-surface requires the sharp.