Elfverson & Co is a yo-yo manufacturer based in Sweden. Only one yo-yo is produced, the Kalmartrissa, which has been in production since 1932. This model is claimed to be the longest running yo-yo model in the world.
The company has manufactured yo-yos on behalf of many other yo-yo companies since its inception. Notable among companies that outsourced some production is Cheerio, which from 1958-1964 outsourced the production of the Cheerio Rainbow and Cheerio Big Chief yo-yos to Sweden. Elfverson also made yo-yos for Royal, Festival, and American Spinners, among others.