Number 3 pencils are harder than No. 2 pencils, creating a lighter, but less variable line. Number 3 is quite often the choice of draughtsman and engineers because the writer has a bit more control over the line.
These vintage pencils are from the mid-20th century and were emblazoned with the logo,
and the company name,
United States Steel
At one time, US Steel was one of the largest employers in the Western Pennsylvania area. The company has undergone many changes since way back when, but the pencils remain.