5/8 inch drive
Here is a brass tag 1928 set. The extensions are square – these switched to round shaft extensions in 1929 (see the example above)
The Brass Tag period is 1927-1932, but these sets seem to stop using the brass tags around 1929/30. This is about the same time Snap-on moved to Kenosha.
The catalogs show this 8-year run, but the tools had a much longer life as a discounted tool for industrial users. A “P” series 5/8-inch drive with the same design sold through 1970.
The “P series” are extended life production runs for sales into industrial users. Typically not listed in the automotive catalogs, they exist and provide an interesting window into “obsolete” tool types that live on in a stealthy way – under the radar, but still out there.
Here is a 1928 set the extensions have square shafts, the finish is Nickle. Both sets have the optional ratchet.