Small mechanical watches of the 1920s to 1950s, built in the geometry of the Deco years: rectangular, square and tank-shaped cases made for the wrist just as the wrist was taking over from the pocket.
Case metals are named a dozen ways in these titles on Sellingantiques: 9ct, 10k, 14ct, 18ct, platinum, silver, chrome, nickel, gold filled and rolled gold.