The operation termed "pening, " is stretching the skin on one side of work to alter its shape, the principle of which is that, by striking the face of the metal with a hammer, the face of the metal struck stretches, and tends to force the work in a circular form, of which the part receiving the effect of the hammer is the outside circle or diameter. The engraving represents a piece of flat iron, which would, if it were well hammered on the face, a a a, with the pene of a hammer, alter its form to that denoted by the dotted lines. Or let the rod, a, shown below be attached to a double eye at one end, the other end requiring to come fair with the double eye, b, at the other end; then, if it is pened perpendicularly on the face, c, of the rod, the stretched skin will throw the end around so that it will come fair with the eye, b. Connecting-rod straps which are a little too wide for the rod ends may be in like manner closed so as to fit by pening the outside of the crown end, or, if too narrow, may be opened by pening the inside of the crown end; but in either case, the ends of the strap alter most in consequence of their lengths, and the strap will require refitting between its jaws.