It's a Thai 10 Satang, I can't quite read the last date digit from the image, it's either 2500 or 2501. I put my stakes on 2501. Here's the triplet to choose from:
Y#79, aluminium-bronze
Y#79a, bronze
Y#79b, tin
It looks like you have the tin one, but if the date is indeed 2501 it must be the bronze one.
By the way, the coin is not that old (1957-1958). The man on the coin is old: 86 yrs now!
Rama IX, aka Bhumibol, is the world's longest sitting head of state (1946 to date)!