Most modern instruments have drawn tone holes. These are the kind you see where the tone hole is formed from the body of the instrument and there is no seam. When the body of the instrument is made it has small holes punched out of the metal. Then a specific diameter metal ball is then drawn up through the hole which widens it and forms the tone hole.
Another technique is to cut the appropriate diameter hole and then place a separate metal ring which forms the wall of the tone hole on the body of the instrument. The wall is soldered to the body of the instrument.
The advantage of soldered tone holes over drawn tone holes is their superior ability to hold their shape and not warp because of dents or over time as the metal relaxes. The disadvantage is that on very old instruments, the solder can disintegrate causing leaks.
Pictured above is a soldered tone hole on a Conn bass saxophone I was working on. You can see a massive space has formed between the body of the instrument and the wall of the tone hole. To repair this we simply re-solder the tone hole to the body, filling in the gap.
Although the procedure is simple, usually where there is one un-soldered tone hole there are others and fixing this requires many keys to be removed. An inexperienced repair person my not notice these problems when they estimate the repair job. That’s why it is important to always estimate carefully and use a leak light.