Stanley plane dating guide
That lateral adjuster of a Union looks like the early twisted Sargent, but with a washer type guide like the Ohio Tools or Stanley.The following tables provide a summary breakdown of identifying characteristics and markings of the Bodies, Frogs and Receivers, Lateral Adjustment Levers, and Lever Caps on Stanley’s Bailey line of bench planes.Some were showered with attention by their former owners, others suffered the worst possible abuse.Some owners worked them so hard that they had to replace one or several parts.
There are detailed type studies available, usually starting with type 1 for the first model then going up with every little or major change.
These features are avoided where possible, along with features that appear in only some planes of a given type (i.e. Where possible, the flowchart uses parts that were probably replaced less often, such as frogs, depth adjustment screws and lateral adjustment levers.
This approach doesn't guarantee that you'll date your plane correctly, as the flowchart can be thrown off by some hybrids.
I've converted some of the plane dating information found in Patrick Leach's Plane Type Study into an easy-to-use hypertext flowchart.
Hopefully by answering a few questions about your plane you can determine which type it is.