A device comprising an annular seal having an annular projection engaged into a groove in the edge of the watch glass is disclosed. The lower part of the seal, said lower part having a bulge, engages onto a surface of the housing and is compressed radially by the bezel. The inner lateral surface of the bezel, said surface being fitted around this seal, comprises two concentric cylindrical surfaces of different cross sections, the surface of larger cross section being that which is adjacent to the base of the bezel, these cross sections being slightly smaller than the cross sections of the outer lateral face of the seal and of the bulge in the non-compressed state. The base of the outer lateral surface of the upper part of the housing has a groove in order to receive a portion of the seal, said portion being deformed by the bezel, thus ensuring the axial blocking of this seal.
A method of case hardening an article formed of titanium, zirconium or an alloy of titanium and/or zirconium is disclosed. First, the article is heat-treated in an oxidizing atmosphere at a temperature in the range of 700 to 1000.degree. C. so as to form an oxide layer on the article. Then, the article is further heat-treated in a vacuum or in a neutral or inert atmosphere at a temperature in the range of 700 to 1000.degree. C. so as to cause oxygen from the oxide layer to diffuse into the article.
