Stanley made these levels in 3 grades, sizes from 6" to 24", for 50 years or more.
Combination general wood and metalworking was the product target market.
Very accurate for woodworking and marginally accurate enough for metalworking.
Yours is a middle grade.
Stanley's cheapest and by far the most common were open end levels. The last 3" of metal at the top and bottom unsupported. These had the shortest and cheapest vials. You can't give these away now.
Yours is the I-beam model. The ends are closed, but only partly. They had longer better vials.
The top line has fully boxed ends and the long vials have rotating Eclipse covers that spin around and cover the vial completely for travel.
None of them have much of any collector following. I like them anyway, myself. I believe the day will come when are collected hotly.
I am looking for a 24" box end top grade, in fine condition, now, before the collector hordes drive the price up. I'd like to have a 6" too. I have 9 and 18".
yours Scott