TY  - RPRT
TI  - Letter Circular 444: hardened copper (revision of Letter Circular 61 issued April 26, 1922, and revised March 19, 1927)
PY  - 1935
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 444r1935
DO  - 10.6028/NBS.LCIRC.444r1935
ER  -