Abstract: A plunger having a generally converging distal portion, and a rear face on which is provided a coupling structure. The coupling structure is transversely engageable by, and transversely disengageable from, a driving mechanism of a power-driven angiographic syringe, and, one engaged, cannot be disengaged by rotation of the driving mechanism relative to the plunger in the absence of translational movement of the driving mechanism and plunger relative to one another. The coupling structure may include a rearwardly extending wall to which is joined a radially inwardly extending flange. The coupling structure may be generally C-shaped, with a continuously curved portion having an arc length not exceeding about 180.degree., and optionally may have tangentially extending end segments respectively joined to the continuously curved portions.