KnifeSol steel spacers are in 9CrSi material and have the same tolerance’s (flatness and parallelism) like circular knives. We belive that the spacer should have the same hardness at core as the circular knives. This especially, to maintain the same feature on the shaft. More and more the tools (Knives, spacers, rubber bonded steel spacers) are mounted and fixed on the shaft with a very high load. Our spacers must therefore resist these loads. But the most obvious reason is that the spacers have to resist for long time, so we also consider the possibility of an incorrect handling due by the workers that could easily damage the spacer, if they were not hardened at core.