The present invention relates to a well tool device (1). A housing (10) has an inner surface (11) defining a through bore (12). A frangible disc (20) comprising upper and lower chamfered supporting surfaces (20a, 20b) and is supported by a seat (40) in relation to the housing (10). A force transmitting device (30) provided is between the frangible disc (20) and the seat (40). The force transmitting device (30) is comprising an upper contact ring (31) provided between the upper chamfered supporting surface (20a) of the frangible disc (20) and the seat (40) and a lower contact ring (35) provided between the lower chamfered supporting surface (20b) of the frangible disc (20) and the seat (40).
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