by grafla » 8 Nov 2019 7:29
I've been looking for a definitive answer about whether there are equivalent sizes between imperial and metric pin diameters.
I did a few tests:
1) I bought a bunch of 2.8mm and 3.0mm pins from a UK locksmith and took some measurements with calipers.
For 6 randomly chosen "2.8mm" pins, the diameter ranged from 2.922-2.928mm
For 6 randomly chosen "3mm" pins, the diameter ranged from 3.102-3.105mm
It turns out that those "2.8mm" pins are actually 0.115" (2.921mm), which is the standard US size. The "3mm" pins are actually 3.1mm, corresponding to 0.122" (This pin size does not seem to be used in the US)
2) I measured 3 pins from a moderately used Australian made Lockwood padlock (which would presumably use metric sizing).
They ranged in size from 2.900-2.917mm, which is slightly smaller than the "2.8mm" pins above - the difference could be partly due to manufacturing tolerances, but is probably just wear and tear.
3) I tried swapping out the padlock's driver pins for the new ones. The "2.8mm" pins fit in easily while the "3mm" pins fit into 4 / 6 of the holes.
One of the holes that the "3mm" pins didn't fit was unused, so it's apparent that the difference in diameter is due to wear and tear.
4) I measured another batch of driver pins and got diameters of 2.781-2.786mm.
So it seems like 2.8mm is actually a distinct size!
The main takeaway from all of this is that 0.115" and "2.8mm" pins are distinct sizes, although 0.115" pins are sometimes sold as 2.8mm.
The tolerances are probably large enough that they can be used interchangeably, especially in repinning where the holes have increased in size.
Additionally, many used locks can be repinned with "3.0mm" - I suspect they should used if they fit because less slop gives better security.
