Because of wear it is often difficult to see which number is stamped, so the # symbol before the patent number is sometimes the only way to tell.
There are also a number of lighters where the lighter is stamped on both the top and the bottom and I have heard reports of lighters with the correct patent number on one end and the wrong patent number on the other. In 1943 this was altered to a 3 barrel with the centre barrel being longer than the two outer barrels.
Both Brass and Chrome became scarce and Zippo had to use other materials.Most lighters fabricated between 19 can be identified by style and model and the patent or patent-pending marks.The appearance of the word "Zippo" in the bottom stamp provides another clue to dating.The obvious choice was Steel, but this presents two problems.Firstly, it is porous and secondly it is susceptible to rust.Due to the scarcity of these lighters it is not possible to document all models/variations here The first lighters made by Zippo were much squarer than those seen today as originally the lighter cases were made from tubing with the base soldered on. All early lighters had either a flat (1933-1941) or a round (1942-1946) bottom.The "Canned bottom" (where the base of the lighter is indented) first appeared in 1946 The lighters above were made from a rectangular tube, with the bases soldered on.Like lighters from other years, there are significant variations in the manufacturing process that can help determine the exact year of production.Unfortunately I do not have the time or the money to build up a collection that will allow me to make the comparisons seen on the rest of the dating pages.These lighters have either a flat or a rounded out bottom and are still stamped with the Zippo logo, although this is not visible unless the paint has worn off.Some lighters in this period were incorrectly stamped with the patent number #203695, the second 2 being missed out in error.