Plomb Wrench and Stamped Sockets

[Provincial]

I found this Plomb wrench in a mixed bag I bought recently.  It is a 3/4" hex box end that is thick at the hex.  It appears to be hand stamped with "PLOMB" between two stylized plumb bobs.  The bobs are quite pointed and the upper end looks like a + mark. 

There were two stamped sockets in the same box.  Both are 13/16" hex and have a 3/4" hex drive.  I haven't seen hex drive stamped sockets before.  One is as-stamped and is closed-end on the drive end.  The other is open-end on the drive end and has been turned to be round on the outside diameter.  The drive of both sockets matches the bearing area of the wrench.  Both sockets fit a standard spark plug perfectly.

Any ideas on age and purpose?