The Christian Brothers rule actually set down precise specifications for the strap.
“No instrument of punishment is to be used in the schools except a strap of leather, that is not to exceed 13 inches in length, 1.25 inches in width, and 0.25 inch in thickness.”
No reference to any official additions of weights.
In my collection of reference material, I have nine pages of notes I made while reading a thesis on corporal punishment as administered in Christian Brother schools – “‘A Most Unenviable Reputation’: The Christian Brothers and School Discipline Over Two Centuries”.