It frequently happens during the construction of a building that some heavy piece of material, such as a roof truss, already placed roughly in position, has to be brought to its exact location. In such case the bottle-jack (Fig. 221) will be found of great service. Given a firm base upon which to rest, the bottle-jack, operated by one man, can raise and sustain in position a weight of from 2 to 3 tons. The same force can be applied to any object, either upwards, downwards, or obliquely by its means. It will be seen from the foregoing that its uses are many and varied. Its total lift is, however, necessarily limited to about 1 foot, in order that it may not become too cumbersome to handle. It consists of four parts; the head (A) having its top side notched so as to grip the object to which the force is to be applied, and its lower side turned down to a shoulder and loosely fitted into a corresponding recess in the top of the round head of the screw (B). This is necessary in order that the screw may be turned, by means of the holes bored through the rounded part, while the head (A) remains stationary as regards the turning movement. The screw (B) is generally square threaded as shown, and of mild steel, and is actuated by passing the "tommy"-bar (D), a steel rod about 18 inches long, through the holes before mentioned.

The Bottle Jack 253

Fig. 221.

The body or "bottle" (C) is of cast iron, and contains a female thread through which the screw (B) passes. A handle is sometimes added, making the jack more portable and easily held in a slanting position when necessary.