In the spirit of GWiens2001 post "What Is Inside an S&G 6730 Safe Lock?" (https://www.lockpicking101.com/viewtopic.php?f=36&t=62460) I decided to share some pictures of a slightly different type of an old safe I got my hands on. My exposition (or expertise) here is not nearly as thorough as GWiens2001's, and if the terminology is not familiar you should probably read his post first. Furthermore I am not a professional, barely an amateur, so please feel free to correct any terminology or other deficiencies I have.
I don't know if there is some actual difference in fashion across the Atlantic or if it's just chance, but I seem to have seen S&G 6730 -type dial-only locks mostly in the states, whereas in Europe (or in Finland at least) the combination safes I've met often also have a handle or a key that operates the locking bar. Anyway, the extra key/lever makes other parts of the mechanism a bit different and alters some behavior of the safe.
Here is the front of the safe, a diplomat MC-350, the text in top-left is just a sticker telling that the safe has passed some security standards of the Swedish government. The keyhole is for a pin-tumbler lock, which I didn't try to pick yet but seemed quite standard and the dial is for a four-number combination.
The interior of the door has a plastic cover shielding the locking mechanism. (The sticker in the up-right corner is again assuring you of the unpenetrability of this safe by fire or foe.) Behind the cover we find the locking mechanism itself. On the left we have four wheels in a stack, with the number dial connected to the top wheel you see in the picture. The wheels behind are slightly smaller but otherwise similar disks with a large slit in one point and a peg in one of the thirteen holes in the outer rim. Somewhat similarly as with the S&G 6730-lock, the wheel attached to the dial can be directly rotated, but the disks behind it are only moved when the peg in the disk above contacts their peg. To change the combination of the safe you simply change the position of the peg on each of the four wheels. (Which means taking apart the stack.)
On the right side of the stack of wheels, the large Y-ish shaped large piece of metal slides left or right when the key is turned, pulling in the bolts you see peeking out of the door on the far right. Currently the stack of wheels is in the "open" position and turning the key freely moves the bolts in or out.
On a close up of the stack with the key in the "open" position we see that the fence has slid into the slots of the wheels. As mentioned above, the wheels behind are slightly smaller but otherwise similar to the outermost disk. Hopefully in the future I'll have a chance to take the wheel stack apart as well to show more details.
Similarly to the S&G 6730 -lock the safe is opened by first dialing the combination, but instead of turning the dial to open the lock you turn the key to pull the bolt in. Thus we can see that since the dial is not responsible for pulling the bolt in, it doesn't matter which way around the combination is dialed. This means that for any combination A - B - C - D starting with a clockwise turn there is another combination X - Y - Z - W starting with a counterclockwise turn. The combinations will have the same last number (D = W) as the topmost wheel is directly controlled, but the numbers X, Y and Z will differ by an amount that you can calculate if you know the size of the pegs that connect neighboring wheels. (Left as an exercise to the reader.)
Finally, a few differences between the Diplomat MC-350 and the S&G 6730 that pop immediately to mind:
- The mechanical structure of the Diplomat is (much) simpler than that of the S&G. In the Diplomat the most delicate part is the mounting of discs on an axle.
- Changing of the combination in the S&G is (much) simpler than in the Diplomat. In S&G you have the change key which you can teach to anyone who knows how to operate the safe. In the Diplomat you need to disassemble most of the lock and you have to understand how the lock works. And you might get grease on your hands. This means that a change of the combination probably requires a locksmith.
- In the Diplomat each wheel has only 13 positions to place the pegs. This means that there are actually only 13^4 = 28,561 different combinations that you can use, instead of the 100^4 = 100 million that you might guess from having a dial 0-100.
- There are no anti-tampering devices on the Diplomat. You can drill and hammer all you want and the lock works unless you break a part of it.
This type of safe is called a direct entry safe. The bolt is operated by the key instead of a lever.
