As soon as the head of a nail is worn off, the shoe becomes loose, therefore a flat-headed nail such as a carpenter drives into wood is of no use to a farrier. The horse-shoe nail head must be countersunk into the shoe so that it wears with the shoe and may retain it in position until quite worn out. The nail has a wedge-shaped head. It has a flat shank, because the thickness of the wall into which it is driven is limited. The hole in the shoe must be made to fit the head of the nail, and as the size of nail most suitable for a hoof varies considerably, it is necessary to make the nail-holes in a shoe very carefully correspond to the head of the proper sized nail. Nearly all hind shoes and some front ones are provided with nail - holes by stamping through them a series of four-sided tapered holes of the size required. Most fore-shoes are "fullered", i.e. a groove is sunk round the shoe close to the outer edge, and through this the holes for nails are afterwards punched. Both methods admit of nails being easily driven with safety. The number of nail-holes really required to retain a shoe should vary with the size of shoe. Never more than eight are required. Usually seven are sufficient for the largest shoe. Small shoes are safely retained by six. The position of nail-holes is important. The wall at the heels is thin, and therefore if good hold of the front portion of the foot can be taken it is unwise to drive any nails at the back part. Nail-holes should not be too near to the outer edge of a shoe, as when the nail is driven insufficient hold is afforded it, and the hoof is likely to be split.
A preferable form.
Fig. 637. - Calkins.
Fig. 638. - Nail-holes.
HACKNEY MARL, LADY KEYINGHAM.
Sire, Danegelt 174; dam, 2016 Dorothy by Lord Derby II 417. The Property of Sir Walter Gilbey, Bart.
Still more important is it that nail-holes should not be placed too far from the outer edge of a shoe, as then a nail is forced to approach too near the sensitive structures within the hoof. The nail-holes at the toe may be a little " coarse", but the holes at the heels must be "fine". The "pitch" or direction of a nail-hole is important, because it controls to a great extent the direction in which a nail can be driven through it. The safest "pitch" for a nail-hole is straight through the shoe, but the holes at the toe should have a little inclination inwards, as the wall at the corresponding part of the hoof slopes considerably, and the nail must follow its direction.