The invention relates to a base strip (1) made of silicone with an upper side and a substantially planar underside, wherein the underlay strip (1) has at least two raised bearing surfaces (12) on the upper side, wherein the bearing surfaces (12) each have a raised profile (13 ), and wherein the underlay strip (1) has a trapezoidal cross-section (11), the base of which forms the underside of the underlay strip (1).
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