| 摘要 |
A magnetic tape cartridge has a reel which includes an upper reel and a lower reel which are plastic moldings, the lower reel being welded to the upper reel by ultrasonic welding. In the shoulder of a boss section of the upper reel, a plurality of recesses are formed in such a manner that the recesses are radially outwardly extended from the center of rotation of the upper reel, and on the surface of the lower reel which are confronted with the recesses, a plurality of welding ribs are formed so as to be engaged with the bottoms of the recesses.
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