Be very careful buying them on eBay.
95% of them are Russian Jupiter-3 lenses that have been very skillfully changed to "Zeiss Sonnars".
The real thread mount Zeiss Sonnars are extremely rare, and a lot of them were made in wartime with very flimsy lens barrels and poor QC.
When the Ukrainian forgers realized that LTM Sonnars were going for high prices, they began creating new engravings for Jupiters. (which are Sonnar copies anyway). Suddenly, several dozen "Sonnars" began to appear on eBay every month, at crazy prices.
Occasionally, you will also get a pre-war Contax Sonnar head grafted onto a Jupiter barrel, with horrible focus collimation or no infinity focus at all.
It's almost impossible to tell which wartime "Sonnar" is real or not.