This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A photograph or manuscript may be sent through the mail unmounted without the danger of being broken by placing it in a tube made as follows: For an 8 by 10-in. photograph procure a piece of cardboard 6 by 10 in., plain mounting board preferred, and cut halfway through the card in three places as shown by the dotted lines in Fig. 1. Then fold it in a triangu'lar shape as shown in Fig. 2. It is easy to make such a tube to fit any photograph or manuscript to be mailed. - Contributed by A. H. Schaefer, Buffalo, N. Y.
Ill: The Bends in the Cardboard are Made on Lines Equal Distances Apart to Form a Triangle