US Patent 9579463 Barrel for syringe and pre-filled syringe

A syringe barrel includes an barrel main body having a cylinder tip at a distal end of the barrel main body; and a cap detachably attached to the cylinder tip by threaded engagement to seal an opening of the cylinder tip. The cylinder tip comprises at least one projection that projects radially from an outer periphery of a proximal end part of the cylinder tip. The cap includes a cylindrical cover that covers an outer periphery of the cylinder tip. A proximal-side inner periphery of the cover comprises a reduced radius portion, and, when the cap is threadedly engaged with the cylinder tip, a distance from a rotation axis of the cap to the reduced radius portion is smaller than a distance from the rotation axis to an outer end of the at least one projection.