4.1.2 Steel spacer(s), to provide the required compression.
The spacer(s) shall be of such size and shape that contact with the compressed test piece is avoided.
The height of the spacer(s) shall be chosen so that the compression applied to the test piece is
(25 ± 2) % for hardnesses below 80 IRHD;
(15 ± 2) % for hardnesses between 80 IRHD and 89 IRHD;
(10 ± 1) % for hardnesses of 90 IRHD and higher.