A method for completion of an oil or gas well with production tubing (14), and a well tool device (1) comprising an first pipe part (20) and a second pipe part (22) each having a first end (20a, 22a), and a second end (20b, 22b) with a through channel (30), said well tool device (1) having a groove (24) provided in an interface in the through channel (30) between the first pipe part (20) and the second pipe part (22), wherein said groove (24) is accommodating a breakable obturator seat (10) made of brittle and tempered glass.