(Click photos for a larger version.)
Pencil-making in 19th-century America is part history and part folklore. William Munroe is often cited as one of the earliest American pencil manufacturers, along with the Thoreau family, Ebenezer Wood, Horace Hosmer, and Benjamin Ball. But there was also the lesser-known David Hubbard, and an unnamed woman (sometimes referred to as a “schoolgirl”) from New England who purportedly removed the center from some twigs then filled them with a mixture of graphite and glue.
By the 1800s, the Conté/Hardmuth method of mixing graphite and clay was being exploited by pencil-makers in America, though the results were hit and miss. Added to this, leads were often off-center, length and width varied from pencil to pencil, and some might be better described as being “round-ish” than “round.” This was due in part to their design—rather than gluing together two symmetrical halves a channel was cut for the lead, which was later capped or plugged, then the pencils were rounded. Here is an illustration from The Pencil by Henry Petroski:
The pencils here have round leads rather than square leads, but you can see the channel with the plug removed:
I’m not certain of the manufacturer just yet, and I may never know. But the way they were made points to a certain time period, and comparing them against known exemplars could help narrow things down. I have a chief suspect, but there’s more work to do.
An early example of an attached eraser: the ferrule is a thin piece of paper, colored blue on one side, which wraps around three times. The end of the pencil was narrowed slightly so the ferrule is more or less flush with the barrel:
Contrapuntalism 
Thank you for showing these precious pencils! – Do you know which kind of wood has been used for them?
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I’m pretty sure they’re cedar.
Though it didn’t show up in the photo there is a slight rotational pattern on the pencils, which looks like how they were rounded. I’d like to know which tool or tools were used to do this.
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Thank you for these additional details! The pattern is unusual – yes, maybe it comes from the tool which was used to round them, but I have no idea which one it could have been.
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This is an excerpt from the article “Pencil Making in Keswick.” It has been printed in several places, but this one is from The Illustrated Magazine of Art, 1854. It’s my understanding that a lot of the early pencil-makers developed their own methods and machinery, but that they were kept mostly secret. So the description in the article may not necessarily describe how all pencils were rounded in the mid-19th century, but it might be a good clue. And since it seems many of the early pencil-makers had a background in cabinetry, perhaps they used common tools that were eventually customized.
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