The invention relates to an assembly comprising—an inserter (10) for insertion of a penetrating member (7) into a patient,—a penetrating member attached to the inserter (10) before use,—a base part comprises a position shaped to receive the penetrating member where the penetrating member can be attached to the base part during use and fastening means (2) which can provide for the base part to be attached to the patient, where the inserter (10) comprises inserter attachment means (14) locking the inserter (10) to the base part before and during insertion of the penetrating member (7) which inserter attachment means can be unlocked so that the inserted can be removed from the base part after insertion of the penetrating member (7), the inserter attachment means comprise at least one protruding part and at least one corresponding opening. Either the at least one protruding part or the at least one corresponding opening part is positioned on a surface of the base part and a corresponding part either comprising a protruding part or an opening is positioned on a surface of the inserter.