A method of anchoring a first object in a second object, the method comprising the steps of: providing the first object comprising a first material and providing the second object comprising a second material, wherein the first material is solid and comprises thermoplastic properties and wherein the second material is solid and is penetrable by the first material when in a liquefied state, the second object having an insertion face, wherein the second object comprises an opening having a mouth in the insertion face, the opening having an opening axis, and the first object further comprising an insert portion, placing the first object relative to the second object so that the insert portion reaches into the opening or is placed about the mouth thereof, anchoring the insert portion of the first object in the opening by transferring energy suitable for liquefaction of the first material to the first object in an amount and for a time sufficient, for at least partial liquefaction of the first material and interpenetration of the first and second materials in the vicinity of the opposite surface areas; stopping the transfer of energy for a time sufficient for the first material liquefied during the step of anchoring to re-solidify, characterised in that the second object, around the opening, has an anisotropic strength with respect to forces perpendicular to the opening axis, and in that a cross section of the opening perpendicular to the opening axis and a cross section and orientation of the insert portion are adapted to each other so that upon insertion of the insert portion in the opening the opposite surface areas of insert portion and opening are pressed against each other by a pressing force that varies around the circumference of the opening, the pressing force between the opposite surface areas acting in a direction (y) of smaller strength of the second object being smaller than the pressing force acting in a direction (x) of larger strength. providing the first object comprising a first material and providing the second object comprising a second material, wherein the first material is solid and comprises thermoplastic properties and wherein the second material is solid and is penetrable by the first material when in a liquefied state, the second object having an insertion face, wherein the second object comprises an opening having a mouth in the insertion face, the opening having an opening axis, and the first object further comprising an insert portion, the second object having an insertion face, wherein the second object comprises an opening having a mouth in the insertion face, the opening having an opening axis, and the first object further comprising an insert portion, placing the first object relative to the second object so that the insert portion reaches into the opening or is placed about the mouth thereof, anchoring the insert portion of the first object in the opening by transferring energy suitable for liquefaction of the first material to the first object in an amount and for a time sufficient, for at least partial liquefaction of the first material and interpenetration of the first and second materials in the vicinity of the opposite surface areas; stopping the transfer of energy for a time sufficient for the first material liquefied during the step of anchoring to re-solidify, characterised in that the second object, around the opening, has an anisotropic strength with respect to forces perpendicular to the opening axis, and in that a cross section of the opening perpendicular to the opening axis and a cross section and orientation of the insert portion are adapted to each other so that upon insertion of the insert portion in the opening the opposite surface areas of insert portion and opening are pressed against each other by a pressing force that varies around the circumference of the opening, the pressing force between the opposite surface areas acting in a direction (y) of smaller strength of the second object being smaller than the pressing force acting in a direction (x) of larger strength.