What the Duncan "Imperial" yo-yo was to the USA, the one-piece Elfverson "Olympic" yo-yo (and "Pro" model) was to Canada. These classic wooden yo-yos were typically a Canadian player's first introduction to yo-yo.
National Yo-Yo and Bo-Lo Company of Toronto, Ontario sold the Olympic and Pro yo-yo between 1968 and 1977. During that time, approximately 2 million Olympics and 3.8 million Pro Tournaments were made. Both models underwent a few changes in stamp design during the nine year run, but the body shape remained the same for both.
Both the Pro and Olympic models continued to be sold under various toy company names--with only slight changes being made to the seals over the years--until about 2005. The yo-yos were manufactured by Elfverson, based out of Sweden.
The Olympic model was sold standalone from a retail counter display box. It was also sold mounted on bubble blister cards as seen here..
Compare with similar versions from Parker, Canada Games, Playtoy, and Irwin Toys.