The unit on the left is the typical one represented in many collections. Most all of these were found on the Nooksack Falls line in north-western Washington State in the late 1990's . The line having been built in 1906-07 .
The unit on the right is older and is from late 1903-04 . these were used primarily on the Electron -Tacoma transmission line (1904) in Washington state and the Mullen extension of the Spokane- Burke Id. line also from 1904. These early units are pretty much unrepresented in collections . These have very drippy caramel glazes as opposed to the more sharply contrasted mottled or all "Thomas yellow mustard " glazes