If you use larger wire, the engine will require more current from the battery. If you use finer wire, a battery of a higher voltage will be necessary. The current consumption will, however, be less. *The Frame.*—The electromagnets are mounted in the frame of the engine by means of two screws passing through the holes E and D. The details of the frame are illustrated in Figure 146. It is made of a strip of wrought iron or cold rolled steel, nine and one-quarter inches long, an inch or an inch and one-eighth wide and one-eighth of an inch thick. The material for making this part of the engine and also the bearings can probably best be obtained at some blacksmith shop or hardware store. Heavy galvanized iron can be used but it is not usually thick enough and it may be necessary use two thicknesses. The ends of the strip are rounded and bent at right angles so as to form a U-shaped piece with sides one and three-quarters inches high. The holes D and E should be large enough to pass an 8-32 screw. The holes A, B and C should be about one-eighth of an inch in diameter. They are used to pass the screw which hold the frame of the engine to the wooden base. [Illustration: FIG. 147—The Bearings.] *The Bearings* are shown in Figure 147. They are U-shaped and are made out of a strip of iron or steel in the same manner as the frame of the engine but are three-quarters of an inch wide instead of an inch and one-eighth. The dimensions will be understood best by referring to the drawing. The 3/32 inch holes near the top of each side are the bearing holes for each end of the shaft. The one-eighth inch holes below are used to fasten the brush holder in position. The holes in the bottom serve to fasten the bearings to the base. [Illustration: FIG. 148.—Details of the Shaft.]