A few weeks ago I bought two pairs of 4 to a plate mandolin machine heads from China off Ebay to make a Tahitian uke or two. Measured my first set and a bit odd the posts were 1/4 inch and 1inch apart on the plate. No worries fitted them and they worked fine.
I just pulled out the second set, pulled out my calipers to check them. 6mm posts 25mm apart. That could have been slightly embarrassing. At first glance they look identical.