This is an uncommon piece! These small stoneware flasks were used to sell servings of tea at train stations in Japan in the early to mid-20th century. The flask's lid doubles as its cup. This one is by Tokaken Co. Ltd, founded in 1888 and still today serving ekiben, or travel lunches, at several stations. This particular flask is from the Odawara Station, which was the company's first location.
The jar is glazed in a yellow ash glaze with iron oxide decoration. On one side it is stamped at the top with 小田原 (Odawara) and 東華軒 (Tokaken) down the middle. On the reverse it says お茶 (ocha, green tea).
Dimensions (approximate): 2.4375" (6.2cm) across, 4.25" (11cm) tall
Volume: 186ml to the brim of the flask