Patent ID: 7419115

Claim:
A magnetic tape cassette having: a base with an opening for accommodating a transparent window and at least one reel of magnetic tape; and a transparent resin-made window member to close said opening in said base, wherein said base and said window member are each composed of materials having no compatibility or having an extremely low degree of compatibility to each other for ultrasonic or thermal welding, said opening in said base has a ridge that engages said window member, said window member has a recess in at least one of two sets of opposed sides which fit said ridge on said base, and wherein said ridge on said base is fitted into said recess in said window member, said base comprising an inner peripheral wall forming the opening, said inner peripheral wall having said ridge, such that portions of said inner peripheral wall above and below said ridge face into the opening, said recess of said window member engages said ridge, such that portions of said window member above and below the recess abut respectively against said portions of said inner peripheral wall above and below said ridge, and said window member has a first side and second side which extend across the opening, and said recess of the window member engaging said ridge is positioned such that a shortest distance from said recess to said first side of said window member is shorter than a shortest distance from said recess to said second side of said window member.