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  <xs:element id="mg_OtherLongTermDebtMember" abstract="true" name="OtherLongTermDebtMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_AssetsAndLiabilitiesLesseeTableTextBlock" abstract="false" name="AssetsAndLiabilitiesLesseeTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="mg_OtherProductsandServicesMember" abstract="true" name="OtherProductsandServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_SeveranceandLaborDisputesMember" abstract="true" name="SeveranceandLaborDisputesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_RevenuePracticalExpedientIncrementalCostOfObtainingContractMaximumPeriod" abstract="false" name="RevenuePracticalExpedientIncrementalCostOfObtainingContractMaximumPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantProFormaFundedDebtLeverageRatioDueToBusinessAcquisitions" abstract="false" name="DebtInstrumentCovenantProFormaFundedDebtLeverageRatioDueToBusinessAcquisitions" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardLastDayTradingPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardLastDayTradingPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_DebtCovenantPeriodSixMember" abstract="true" name="DebtCovenantPeriodSixMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies" abstract="false" name="LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_RightToCustomerContractsMember" abstract="true" name="RightToCustomerContractsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_DebtCovenantPeriodAxis" abstract="true" name="DebtCovenantPeriodAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="mg_OfficeFurnitureAndEquipmentMember" abstract="true" name="OfficeFurnitureAndEquipmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_NumberOfEmployeeShareBasedPlans" abstract="false" name="NumberOfEmployeeShareBasedPlans" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment" abstract="false" name="DebtInstrumentCovenantFundedDebtLeverageRatioForAdditionalInterestPayment" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit" abstract="false" name="LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantInterestCoverageRatio" abstract="false" name="DebtInstrumentCovenantInterestCoverageRatio" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_TexasCustomerMember" abstract="true" name="TexasCustomerMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_AcquisitionRelatedCostsAndFairValueAdjustmentsToInitialPurchasePriceAllocation" abstract="false" name="AcquisitionRelatedCostsAndFairValueAdjustmentsToInitialPurchasePriceAllocation" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DebtCovenantPeriodFourMember" abstract="true" name="DebtCovenantPeriodFourMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_IncreaseDecreaseInOtherAccruedLiabilitiesAndDeferredLiabilities" abstract="false" name="IncreaseDecreaseInOtherAccruedLiabilitiesAndDeferredLiabilities" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantPrepaymentOfOutstandingCreditFacilityRequiredIfCashAndCashEquivalentsExceedsAmount" abstract="false" name="DebtInstrumentCovenantPrepaymentOfOutstandingCreditFacilityRequiredIfCashAndCashEquivalentsExceedsAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DebtCovenantPeriodTwoMember" abstract="true" name="DebtCovenantPeriodTwoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_COVID19PandemicMember" abstract="true" name="COVID19PandemicMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_LossContingencyNumberOfWeldsAllegedNotInCompliance" abstract="false" name="LossContingencyNumberOfWeldsAllegedNotInCompliance" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_ScheduleOfAccruedLiabilitiesDeferredRevenueAndContingentConsiderationLiabilitiesCurrentTableTextBlock" abstract="false" name="ScheduleOfAccruedLiabilitiesDeferredRevenueAndContingentConsiderationLiabilitiesCurrentTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType"/>
  <xs:element id="mg_TermALoanFacilityMember" abstract="true" name="TermALoanFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_OperatingLeasePercentageOfReductionOfRentalPayments" abstract="false" name="OperatingLeasePercentageOfReductionOfRentalPayments" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="num:percentItemType"/>
  <xs:element id="mg_AcquisitionRelatedContingenciesMember" abstract="true" name="AcquisitionRelatedContingenciesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="nonnum:domainItemType"/>
  <xs:element id="mg_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsIncreaseDecreaseAdjustmentsinPeriod" abstract="false" name="SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsIncreaseDecreaseAdjustmentsinPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
</xs:schema>
