When did Hilerich and Bradsby quit making oil tempered Baseball bats?

"Oil Tempered" is term used for the process of hardening or preserving the wood on Baseball bats. "Bone Rubbed" is a process to harden the surface of the bat and appears on bats made in the 1920s The "Powerized" process was first used, and patented by the Hillerich & Bradsby Co. in 1931 and has pat. pending beneath the stamp. Powerized and Bone Rubbed" was used during the 1932 season only. In 1933 and 1934 you will see it stamped "Powerized and Oil Tempered" which usually is a very light heat foil type print. in 1935 until present, they go with just "Powerized" Flame Tempered is a process of drying and hardening the wood with lower grade baseball bats. If your bat reads "Flame tempered it is a store model bat."Powerized" is used on higher grade bats, and professional models.