What is a "lock pinning tray?" George
Hey George - Do you know how to do web searches on your own, or do you always ask here first?
Standard locks, like the one on house front doors, are called "pin tumbler" locks. There are several small pins inside the lock cylinder where you insert the key. The numbered pins are different lengths, but the differences are small. It is easy to get them mixed up. The order of the pins in your lock must match the length of the cuts (teeth) on your key or the lock cylinder won't turn.
See this link for more, especially the "Modern Mechanism" diagram halfway down the page:
A lock pinning tray
is used by locksmiths and other professionals to hold, sort, and organize the small pins when they rekey locks. They take the lock apart and remove the cylinder, then open up the cylinder to change out the pins so they can match them to another lock, an existing key that you measure, or a "key code" with an ordered list of pin numbers to use in the lock.
A long time ago, I seemed to be the only non-locksmith who knew this stuff. These days, there are lock picking competitions and clubs all over, and it has become a hobby or sport to some people. All of this information is out on the internet.