校准环规，适用于BowersXT系列内径千分尺，详见下表。型号环规XTR3M2.5XTR5M4.00XTR7M5.00XTR8M8.00XTR12M12.50XTR20M20.00XTR35M35.00XTR65M65.00XTR80M80.00XTR125M125.00XTR175M175.00XTR225M225.00XTR275M275.00)