A plug-in piece 1 for sealing connection of two mutually assigned cylindrical surfaces includes an essentially tubular support body 2, which on its ends exhibits annularly encircling sealing elements, which can be made to engage to produce a sealing connection with the cylindrical surfaces to be sealed, wherein at least one of the sealing elements is configured as an annularly encircling sealing bead 3, 30 on the outer surface of the support body 2, with a spherically curved sealing surface. Provision is made that the spherical radius of the sealing surface (3, 30) is chosen so that the center of the sphere is roughly at the axis of support body (2) symmetry. Thus, the compression forces are ensured to remain largely constant, independent of the angular setting over the entire surface of the sealing bead.