It is a sheet metal version of a traditional wooden trap known as a slate trap, I never saw one which actually had a slate as a door but i can see where the name comes from as a slate would probably have been used in the days before sheet metal was available.
I don't know if this type of trap has other names or designs in other regions. If anyone knows of any please post a pic if you can.
These would be traditionally home made from scraps of wood and all kinds of stuff, I remember seeing many different ones when i was a kid back in the 1970's, I googled slate trap and found nothing at all, It may be just a name used in my region of Ireland but the old folks that came into the hardware store i worked in all said that this was the most affective trap for catching rats..
The live rats would have been released in a open yard or grass area and would be given a chance of freedom if they could out run the farms dogs. in the pre TV days would have been a source of entertainment, a source for wagers and a way of showing of how good a dog you had( good dogs would get the rat in less than 2 feet from the trap.
These traps have been replaced but the modern factory made snap traps and wire cage traps. Its not often you meet anyone under the age of 25 who knows what a slate trap is.
Thanks for looking, I hope this record is useful to anyone who has a varmint problem.
I have never seen a commercially available version of this trap. My dad made this around the time he retired and it was built using a very heavy gauge galvanized sheet metal so it would never need rebuilt again in his lifetime.