Most bottle factories mark their bottles with a series of symbols and/or numbers. These are called Punt Marks. If you have bottles with identical punt marks, it is a pretty safe bet they came from the same batch, and would therefore be compatible. Let’s have a look:
Although it’s a little hard to see, there is a factory mark that looks something like a large curvy U followed by 61. Now, when we refer to the Bucher Emhart Complete Punt Mark Library, we see that this bottle comes from:
The Ardagh Glass company in Barnsley UK. Any other bottles we find with that same Punt Mark will MOST likely be compatible. (Always test.) The other number on the bottle is a Line Number, and refers to which furnace the glass was created in.
If you are interested in the technical side of glass, I recommend checking out the other free publications on the Bucher Emhart website. Really cool stuff!