Yonezawa STS was founded in the 1950's and was one of the largest and most creative of all (post-war) Japanese tin toy producers. Some of these toys were marked STS. The origin of this STS label remains unclear, but it could be a toy importer.
It was a large toy maker, producing thousands of different mechanical (friction, clockwork, etc.) but also all sorts of battery operated toys from the 1950's through the early 1970's.
The firm shortly dabbled in RC toys in the mid-1980s with the Wave Hunter buggy (scale 1/10), in North America known as the Monogram Lightning.
It is uncertain what has become of Yonezawa STS, but some believe it is nowadays involved in the manufacturing of (industrial) electronics.