This is a Siegley #3 type 12, which puts it about 1900 = 1901 according to “Plane Makers of Wikes-Barre, Pennsylvania: Jacob Siegley, Edwin Hahn, Keystone Tool Works”
This was probably one of the last runs Jacob Siegley before Stanley bought him out in Aug 1901.
The blank lever cap is different than any I’ve seen so far. Most of the Siegley made planes have the number on the cap. When Stanley bought him out they went to a stippled or checkered type pattern.
This plane weighs 2# 10 ozs