Have turned up some old keys the original one of which has invincible stamped on the bow and looks to have up to 13 possible lever steps, there are also two copies of the same key from chip vine Newcastle, single bitted and the stem of the key looks to have a slight taper on it, 5 guage at the tip, getting slightly thicker as you progress down the bitting, invincible made me think chatwood, but no chatwood name stamped on the bow, just invincible and 29672, any ideas?