The boring rods, Figs. 61, 62, are in 3, 6, 10, 15, or 20 feet lengths, of wrought-iron, preferably Swedish, and are made of different degrees of strength according to the depth of the hole for which they are required; they are generally 1 inch square in section: at one end is a male and at the other end a female screw for the purpose of connecting them together. The screw should not have fewer than six threads. One of the sides of the female screw frequently splits and allows the male screw to be drawn out, thus leaving the rods in the hole. By constant wear, also, the screw may have its thread so worn as to become liable to slip. Common rods being most liable to accident should be carefully examined every time they are drawn out of the bore-hole, as an unobserved failure may occasion much inconvenience, and even the loss of the bore-hole. In addition to the ordinary rods there are short pieces, varying from 6 inches to 2 feet in length, which are fixed at the top, as required, for adjusting the rods at a convenient height. [Illustration: Boring Rods. Fig. 61, 62.] [Illustration: Hand-dog. Fig. 63.] [Illustration: Lifting Dog. Fig. 64, 65.] [Illustration: Tillers. Fig. 66.] Fig. 63 is a hand-dog; Figs. 64 and 65, a lifting dog; Fig. 66, the tillers or handles by which the workmen impart a rotary motion to the tools. The tillers are clamped to the topmost boring rod at a convenient height for working. Fig. 61, a top rod with shackle. Fig. 67, a spring-hook. When in use this should be frequently examined and kept in repair. [Illustration: Spring-hook. Fig. 67.] Lining tubes are employed to prevent the bore-hole falling in through the lateral swelling of clay strata, or when passing through running sand. The tubes are usually of iron, of good quality, soft, easily bent, and capable of sustaining an indent without fracture. Inferior tubes occasion grave and costly accidents which are frequently irreparable, as a single bad tube may endanger the success of an entire boring. Wrought-iron tubes with screwed flush joints, Fig. 68, are to be recommended, but they are supplied brazed, Fig. 69, or riveted, Fig. 70, and can be fitted with steel driving collars and shoes. Cast-iron tubes are constantly applied; they should have turned ends with wrought-iron collars and countersunk screws. [Illustration: Tubes with Screwed Joints. Fig. 68.] [Illustration: Tubes with Brazed or Riveted Joints. Figs. 69, 70.] Cold-drawn wrought-iron tubes have been used, and are very effective as well as easily applied, but their relatively high cost occasions their application to be limited. [Illustration: Stud Block. Fig. 71.]