This is not a random rule. The final determination of this figure is well-founded. The bottle cap first requires good sealing, that is, many folds; At the same time, the bottle cap should be firm, that is to say, the number of pleats should not be too large to ensure that the contact surface area of each pleat is large. 2 1 tooth is the best compromise between these two requirements.
The earliest inventor of this corrugated metal bottle cap is William? However, he found that the best number of teeth for carbonated beverage bottle cap sealing is 24, and applied for a patent for the steel mold designed for this purpose. 1892 On February 2nd, Pater obtained a patent for a metal bottle cap with wavy edges and 24 teeth lined with paper to prevent the beverage from contacting with metal. This 24-tooth bottle cap became the standard for bottle caps in the following years.
1930 or so, steel dies are threatened by cheaper tinplate dies. However, if the new mold still uses 24 teeth, it cannot be patented, so it is changed to 2 1 tooth to avoid infringement on the original design. And 2 1 tooth is the lowest tooth number to avoid beverage leakage.
There are deeper reasons for this change from 24 to 2 1. 24-tooth bottle caps are first placed on the bottles one by one with a foot press. After the automaton appeared, put the bottle cap into a feed pipe, and the 24-tooth cover can easily block the feed pipe. If the number of teeth is odd, this will not happen. Because the sealing performance of 23 teeth is not as good as that of 2 1 tooth, people choose the least number of teeth. Gradually, 2 1 tooth has become a natural choice for manufacturers.