It measures nearly 3cm. Weighs about 8g Bought from a barn sale in Salem, OR from a veteran in the army.
Here's your coin. It's a 5 Sho.http://worldcoingallery.com/countries/Tibet_all.php. Second row, right side.
It's a 5 sho piece from Tibet, but not the one noted above. Your coin is a "three mountains, two suns" piece that was made between 1947-1950. Should be ~8.7g, so 8g would be within tolerance accounting for wear. More info: http://en.numista.com/catalogue/pieces19093.html
I think the picture is the same coin shown in both links by the CT members. The first link has the wrong description in it's wording. Three mountains is correct.