Korby,
Keith's link says it all really.
For what it's worth, one of my customers bought me one in the mistaken belief he'd found a bargain at a boot sale. There seems to be a flood of them on the market and they're all the same plate; they seem a bit too thin to my way of thinking and cast iron doesn't seem to be the correct material. There are a lot of fake plates about at the moment, railway related and otherwise.
Most loco's seem to have brass worksplates although the later 1950's Barclays had aluminium – I have two of these, one on either side of a loco! The Railway Executive/BTC registration plates were usually cast iron as far as I am aware.
Kind regards,
John.
As far a