Nyob rau hauv precision optical shafts, feem ntau yuav tsum tau rau saum npoo hardness.Lub hom phiaj ntawm sab nraud hardness yog los txhim kho hnav tsis kam.Rau cov khoom siv hlau, qhov nyuaj ntawm qhov hardness, qhov hnav-resistant ntau dua.Txawm li cas los xij, qhov nyuaj ntawm cov tub ntxhais, qhov qis dua qhov toughness, thiab qis dua qhov load-bearing thiab cuam tshuam tsis kam.Yog li ntawd, rau cov kev xav tau tseem ceeb ntawm cov ncej: sab nraud hardness thiab sab hauv toughness.