To a Sargent collector, the Sargent 6408 plane is one of the more sought after planes. I never thought I’d ever see one, say nothing about own one.
The 6400 series has only been observed in the 6408 size.
This particular #6408 is shown in “The Sargent Hand Plane Reference Guide for Collectors and Woodworkers”
The one posted in Sargent Plane by the numbers – with Pictures is a different plane but identical. Both have a type 2 cutter, the brass two piece blade adjuster, the 408 and a dot on the back side of the cap.
Interesting note, Bedrocks came out in 1898, and this Sargent #6408 which is a prototype was made in 1906. Production of the first production Shaw patent was around 1910. But it wasn’t until 1911 that Bedrock converted to the flat side and the improved model, so Sargent had the “no blade removing adjustable frog” first.