Locking structures and syringe systems provide increased locking force and/or sealing between a syringe and another syringe or applicator tip coupled thereto. One locking structure includes a tubular member having an interior surface, an exterior surface, and a longitudinal axis extending therethrough, one or more first tabs projecting from the exterior surface of the tubular member so as to at least partially encircle the tubular member, and means for increasing resistance between the one or more first tabs and corresponding structure (e.g., grooves) of a device (e.g., a syringe or applicator tip) that is selectively coupleable to the tubular member.