Hardness of slip gauges should be,

Explanation:

• Slip gauges or gauge blocks are used as standards for precision length measurement.
• Gauge blocks or slip gauges are made of a special steel alloy.
• These gauges are made in sets and consist of a number of hardened blocks made of high-grade steel with low thermal expansion.
• Slip gauges are rectangular blocks of hardened and stabilized high-grade steel or zirconium oxide (ZrO2).
• The cross-sectional size of a slip gauge is 32 × 9 mm means they have 9 mm wide and 30 to 35 mm long cross-section.
• The hardness of slip gauges should be more than 63 HRC.
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