Ross,
The Oil Well Supply Company did not make that die stock. They were manufacturers of oil well rigs, drilling machines (chain and later rotary), and cast and malleable pipes, as the links provided by others show or hint at. In the 1920's, I think they were maybe the largest supplier of oil well equipment on the planet. I remember seeing their ads somewhere in six different languages. If you search their name on Google Books, 1921, I bet you find a ton of neat stuff. But that die stock was made for them.
It looks like a Walworth die stock to me. The same Walworth that made the famous Stillson pipe wrenches.