Magnetic tape cassettes and processes for producing them

A magnetic tape cassette having:

• a base with an opening for forming a transparent window;
• and
• a window member to be installed in said opening, wherein
• said base has in at least a part of an inner circumferential area of said opening a rigid upper window frame, an elastically deformable lower window frame and a temporary fitting portion that allows said window member to be inserted between said upper and lower window frames,
• said window member being made of a transparent resin that is a different material from the material of which said base is made, such that when heat or ultrasonic waves are allowed to act on the window member and the base, the two materials do not substantially mix, and
• said upper window frame or said lower window frame around said opening or said window member is provided with a projection in a position where said upper window frame or said lower window frame contacts said window member, and wherein
• said window member being inserted into said temporary fitting portion so that said lower frame deforms elastically to achieve a temporary joint between said window member and said base, and
• ultrasonic waves or heat is allowed to act on said temporary joint.