The sixpence was part of the now defunct pound, shillings and pence system. The British exported this system to various parts of their empire. Often the size, shape, metal and weight of the various versions of these coins was more or less uniform across the Empire: this can be observed in the shillings, florins and halfcrowns. However, the lower the denomination, the more likely the different coins were to show variations. The sixpence is a nice example, because most of them did match one another in size, shape, weight and metal, and the different designs are interesting to look at. But there were just a few that deviated in one or two ways from the standard.
The silver and cupro-nickel sixpences of the UK and the various countries of the Empire that used it varied slightly, between around 19mm and 19.5mm in diameter. If any sixpence I am displaying falls outside that range, I will say so. I'll start in the 20th century, by showing that the reverse design of Edward VII's sixpence, with a simple wreath, was the same as Victoria's. These images are from our member Tony Clayton's UK coins site.