The operation member (11) has a central opening (17) with a periphery (18) and at least one protruding element (20) arranged on the periphery and extending into the opening, which is surrounded by a protruding rim (21). The protruding rim is interrupted along the periphery by at least one gap (22). If more than one gap is provided, the gaps are arranged such that the pattern of the gaps does not comprise a symmetry that would allow a rotation different from an integer multiple of 360° around a central axis of the opening to map the complete pattern of gaps onto itself. The operation member may be combined with a drive member comprising abutments in positions corresponding to the positions of the gaps.本發明係關於一種操作構件(11)，其具有一擁有一周邊(18)之中央開口(17)以及配置於周邊上且延伸至開口中之至少一突出元件(20)，其被一突出外緣(21)圍繞。突出外緣沿著周邊被至少一間隙(22)所中斷。若提供不只一間隙，間隙係配置使得間隙的圖案不包含一對稱性，其將容許繞開口的一中央軸線作不同於360°的整數倍數之一旋轉，以將間隙的完整圖案映繪至其自身上。操作構件可與一驅動構件作組合，驅動構件在對應於間隙位置的位置中包含抵靠件。
