The capital letters T (top of the bar) and B (bottom of the bar) are used to indicate the position of the thin mold line next to each killer bar, counting from the top bar down.
The following cancel is classified as Type 3 (A-BBT)
The following cancel is classified as Type 3 (AC-TBT)
In 1940, a new killer bar mold was introduced that was slightly narrower than the earlier ones, and had no thin line next to it. The presence of this bar is shown by the letter O. If one or more of the bars has been lost, its position is indicated by the letter X.
The following cancel is classified as Type 3 (A-OBO)
The letters O and X are also used to describe the position of lost killer bars on Type 3 and Type 5 cancels issued before 1931.
The following cancel is classified as Type 3b (AC-OOX)
