A bobbin holder of a yarn winder includes a holder body, a bobbin holding and handling member, elastic members deformable according to the movement of the bobbin holding and handling member, spacers maintaining the elastic members at predetermined intervals and transmitting the movement of the bobbin holding and handling member to the elastic members, and a cylindrical support member attached to a turret and rotatably supporting a drive shaft. The holder body has a boss portion for connection to the drive shaft and hollow portions to accommodate the bobbin holding and handling member and the cylindrical support member on either side of the boss portion. The boss portion has annular projections extending into the hollow portions. Also, the boss portion has at least one portion in which the amount of increase in the inner diameter of the boss portion (d1) and the amount of increase in the outer diameter of the drive shaft (d2) due to a centrifugal force during rotation satisfies the relationship of (d1 - d2) 20 µm.
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