| 摘要 |
To improve a bad appearance due to an interconnection between a pair of disk substrates (20, 30) which are bonded with annular grooves (25, 35) being opposed to each other by a simple structure and at a low cost, which have annular grooves (25, 35) near their center openings (15), an outer groove end (26) of the annular groove (25) of one disk substrate (20) in the radial direction is registered in position with an outer end (36) of the annular groove (35) of the other disk substrate (30) and inner groove ends (27, 37) of the annular grooves in the radial direction are located in different positions. The annular grooves have different groove widths A, B.
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