The Feeler Gauge Tool Thread
My tool was made from a .016" inch thick feeler gauge. I made the finger of the tool .127" wide and used a 1/4 inch drill bit to make the curve on the finger. The tool is designed to snag on the bottom tumbler (representing the first number in the combination). The bottom tumbler contains four vertical posts. These posts are separated by a unique distance apart when treated as pairs. The objective is to position the tool randomly within the lock (second picture) and rotate the dial clockwise. When the dial stops, record the letter or number. Then, remove the tool out of the lock's drain hole about half way (enough to allow movement of the dial clockwise). When the finger clears the post on the tumbler, insert the tool fully into the lock (second picture). Note the next stop point on the combination dial. If the next stop point changes by four clicks, then the first number of the combination is the number first recorded. For example, if the dial stopped at "H" and then stopped again (after manipulating the tool out and inl) at "9". The the first character of the combination is "H". This technique works because the spacing of the posts of each pair is unique and is consistent with all 1590d padlocks. At this point, the tool can be removed.The remaining two characters of the combination are determined by trying every combination past "H" (passing the number once and then landing on it, counterclockwise) and then merely rotating the dial clockwise testing each number with light shackle tension.