Modern padlocks In the early 18th century, Polhem designed and started manufacturing his now-famous padlocks. He was the first to use a new method in Sweden, serial production. He divided up the work so that each of the workers only performed one stage of the lock-making process. In 1737, the workshops and residential buildings at Stjernsund were damaged in a serious fire. The factory was rebuilt and continued manufacturing Polhem locks for the rest of the century. An unpickable barrier lock, the Polhem lock has no springs and has a removable shackle. All parts of the lock were made of iron. In the 19th century, other locksmiths in different parts of Sweden also made Polhem’s Scandinavian lock. Changes were subsequently made: keys were made out of cast iron or brass, a hinge joint was added to the removable shackle, and the smallest Polhem lock was made entirely of brass. “Short Story about the Finest Mechanical Inventions” In 1729, Christopher Polhem wrote a little booklet entitled “Short Story about the Finest Mechanical Inventions,” in which he summarized his inventions to date. He comes across as disgruntled that his padlocks did not receive the acclaim that he had expected. Then some machines were set up for all sorts of locks, which were well filed and polished on all sides. A few hundred of these were made as examples and sent to Stockholm. But, as the smiths in Stockholm viewed these locks with prejudice, they used their Privileges to obstruct the sale of the locks, such that most were returned after a time, covered in rust. Work at the factory also ceased, despite that there was great need and use for this lock when all ordinary locks were inferior to it. My invention was so safe that I was willing to wager anyone a thousand ducats that no one, in any way whatsoever, can pick or use a skeleton key on the locks that I have made, and that cost no more than ordinary locks. It is not known whether Polhem actually made this bet.