Lots of steel stems had that separate doodad under the bolt head, including French and English-made. Annoying when they get lost, though they're prettey interchangeable between brands.

Many better steel stems brazed that part on, like Cinelli and the GB 531.

Here's a Philippe lugged-steel with a doodad that I'm pretty sure is from a different stem, though it works fine.



Here's a Titan stem, the adjustable variant, but that simple lug shoreline is how I remember Titan stems.


Did they also make one with a swoopy lug shape like OP's ? Pics if ya got 'em!