Thanks guys for the very helpful responses.

I found my Nick Stroebel book and the information there seems to confirm that the Lyman 35 and 48 were available pre World War I.

Stroebel lists the patent date for the Lyman 35 as August 15, 1905 but he doesn't mention when production started. However, I think we can assume it started soon after the patent date based on the information he provides about the Lyman 48.

The Lyman 48 was patented on July 11, 1911 and was manufactured continuously from 1911 until the end of production in 1974.

I'm finding that these Lyman sights are a fascinating field for study. These are precision made instruments of very high quality.

I have purchased several rifles over the years that had the Lyman base present, but the slide missing. I have now chased down just about all of these missing slides. The rifles look much better with the complete sight. Of course the sights are much more useful as one gets older.

Anyway, very interesting stuff and some of these old sights are quite valuable. Don't ignore any listings you may see for these sights at reasonable prices.