As I understand it, the little devices added to CDS (Circular Steel Datestamps) to provide rigidity to the cancelling hammer, which also aids us in correctly identifying some hand cancellers.
Possibly most beautifully evidenced on Hungarian stamps..........

Mostly little stars, crosses etc & etc. to the very blunt and aggressive arced black bars on British cancellers.
September 2017
BLOCKS PLATES STONES (No mention of Philately)
Print Matrices/Printing Surfaces in Research and Collection
