Seeing that there are knowledgeable forum members and some across the pond, maybe some light can be shed on bolt threads.

I am working on a 1891 Mosler screw door and it has metric threads. Not modern day metric but old world metrics. I first noticed it with the mounting bolts for the time locks. Luckily, even though I was missing both time locks, I did locate 2 Yale Triple L time locks and both had the mounting bolts included.

Next, on the door pivot bolts, the threads were all damaged as Mosler had hidden lock bolts covered with filler. I discovered this while battling the first pivot bolt but despite drilling and using an easyout on the others they were all damaged as the safe had been taken apart at some point earlier in it's life. The machinist said, "What the hell kind of threads are these?" No matter, he can duplicate anything so he made two new lower pivot bolts (easy to make) and weld repaired and match cut the upper bolts. (difficult to make the whole bolt)

Now I need some new bolts that hold the inner screw door threads. Again odd threads. I picked up a metric thread gauge so I know what I am dealing with and although it tells me the thread pitch, I can't seem to match up to thread charts I find on line.

The current bolt has the old British 11G 55 degree Whitworth thread, not unusual in of itself. What's odd is it is on a ~1/2" bolt and according to Whitworth thread charts that thread is used on a ~5/8 bolt. On another Mosler I have there is a 5/8 with 11G Whitworth threads. Back to the machinist.

So what I am guessing... Mosler cut whatever thread they wanted on the bolts they made?

I also noticed that the bolts in the Yale time lock are also different. Anyone familiar with them?

The point is, if your buying an old safe, beware of missing or damaged bolts. It can get time consuming and expensive for replacements.