The rails form a semicircle at the post, with the ends of the arc pointing down the alley. A tightly stretched leather strap extends horizontally from the upper end of the arc back to the post, where it is fastened with a swivel screw. Half way up, from the points of the arc, a second rail, _i. e._, the “receiver,” is built, with sufficient space between it and the strap to allow the passage of the largest size ball. With the momentum gained by rolling down the incline of the kick-back, the ball rolls back on the inside of the curve until it strikes the strap, where its course is stopped, and it drops on the receiver, ready again for use by the bowler. In beginning the construction of an alley, the mechanic lays the leveling strips on which the bed is to rest. These are set at right angles to the direction in which the bed is to lie, and must be spirit-leveled for accuracy, and firmly fastened to the foundation. A strip of cork carpet is then laid the full width of the alley and extending the entire length of the bed. This is to reduce to a minimum the sound of the balls dropping on and rolling down the bed. On the leveling strips at the extreme side of where the bed is to lie, a 3 x 1-inch maple strip is laid, widest side downward, with its finished one-inch edge nearest to the gutter. One end of this strip marks the extreme end of the approach. The other end of the strip is continued by adding other strips the full length of the bed. When these have been carefully squared to the exact direction the alley is to run, they are fastened to the leveling strips. The next strip, also of maple, is tongued into the lower one, but its continuous length extends only about five feet beyond the foul line, or about eighteen feet from the approach end. A bowling bed cannot be laid as an ordinary floor. It is built upon its side and when finished resembles a wooden wall about seventy-five feet long four inches high and three inches wide. The approach end of the bed, approximately eighteen feet long, is constructed of maple, with each alternate strip of the 3 x 1-inch bed stock about eighteen inches shorter. The pit end of the bed is similarly constructed for a distance of about six feet. The space between is filled in with the pine strips of the same dimensions, and the alternate long and short strips at the inner ends of the approach and pit ends form mortices into which the pine dovetails. [Illustration: PIT END SECTION OF BOWLING ALLEYS] The wear on the bed occurs where the bowler walks and drops the ball and where the ball strikes the pins; hence the hard maple. The interior is filled with pine, which is softer, because it retains a higher polish and prevents the rolling ball from bumping; thus throwing it from its proper course.