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<?xml version="1.0" encoding="windows-1252"?> |
<ownershipDocument> |
| <schemaVersion> X0306 </schemaVersion> |
| <documentType> 4 </documentType> |
| <periodOfReport> 2019-05-08 </periodOfReport> |
| <notSubjectToSection16> 0 </notSubjectToSection16> |
| <issuer> |
| | <issuerCik> 0000098362 </issuerCik> |
| | <issuerName> TIMKEN CO </issuerName> |
| | <issuerTradingSymbol> TKR </issuerTradingSymbol> |
| | </issuer> |
| <reportingOwner> |
| | <reportingOwnerId> |
| | | <rptOwnerCik> 0001013088 </rptOwnerCik> |
| | | <rptOwnerName> PALMER JAMES F </rptOwnerName> |
| | | </reportingOwnerId> |
| | <reportingOwnerAddress> |
| | | <rptOwnerStreet1> 4500 MT. PLEASANT ST. NW </rptOwnerStreet1> |
| | | <rptOwnerStreet2></rptOwnerStreet2> |
| | | <rptOwnerCity> NORTH CANTON </rptOwnerCity> |
| | | <rptOwnerState> OH </rptOwnerState> |
| | | <rptOwnerZipCode> 44720 </rptOwnerZipCode> |
| | | <rptOwnerStateDescription></rptOwnerStateDescription> |
| | | </reportingOwnerAddress> |
| | <reportingOwnerRelationship> |
| | | <isDirector> 1 </isDirector> |
| | | <isOfficer> 0 </isOfficer> |
| | | <isTenPercentOwner> 0 </isTenPercentOwner> |
| | | <isOther> 0 </isOther> |
| | | <officerTitle></officerTitle> |
| | | <otherText></otherText> |
| | | </reportingOwnerRelationship> |
| | </reportingOwner> |
| <nonDerivativeTable> |
| | <nonDerivativeTransaction> |
| | | <securityTitle> |
| <value> Common Stock </value> |
| <footnoteId id="F1"/> |
| </securityTitle> |
| | | <transactionDate> |
| <value> 2019-05-08 </value> |
| </transactionDate> |
| | | <transactionCoding> |
| <transactionFormType> 4 </transactionFormType> |
| <transactionCode> A </transactionCode> |
| <equitySwapInvolved> 0 </equitySwapInvolved> |
| </transactionCoding> |
| | | <transactionAmounts> |
| <transactionShares> |
| <value> 2525 </value> |
| </transactionShares> |
| <transactionPricePerShare> |
| <value> 0 </value> |
| </transactionPricePerShare> |
| <transactionAcquiredDisposedCode> |
| <value> A </value> |
| </transactionAcquiredDisposedCode> |
| </transactionAmounts> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 10620 </value> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </nonDerivativeTransaction> |
| | </nonDerivativeTable> |
| <derivativeTable> |
| | <derivativeTransaction> |
| | | <securityTitle> |
| <value> Restricted Share Unit </value> |
| </securityTitle> |
| | | <conversionOrExercisePrice> |
| <value> 0.0 </value> |
| </conversionOrExercisePrice> |
| | | <transactionDate> |
| <value> 2019-05-10 </value> |
| </transactionDate> |
| | | <transactionCoding> |
| <transactionFormType> 4 </transactionFormType> |
| <transactionCode> A </transactionCode> |
| <equitySwapInvolved> 0 </equitySwapInvolved> |
| </transactionCoding> |
| | | <transactionAmounts> |
| <transactionShares> |
| <value> 2425 </value> |
| </transactionShares> |
| <transactionPricePerShare> |
| <value> 0 </value> |
| </transactionPricePerShare> |
| <transactionAcquiredDisposedCode> |
| <value> A </value> |
| </transactionAcquiredDisposedCode> |
| </transactionAmounts> |
| | | <exerciseDate> |
| <footnoteId id="F2"/> |
| </exerciseDate> |
| | | <expirationDate> |
| <value> 2020-05-10 </value> |
| </expirationDate> |
| | | <underlyingSecurity> |
| <underlyingSecurityTitle> |
| <value> Common Stock </value> |
| </underlyingSecurityTitle> |
| <underlyingSecurityShares> |
| <value> 2425.0 </value> |
| </underlyingSecurityShares> |
| </underlyingSecurity> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 2425 </value> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </derivativeTransaction> |
| | </derivativeTable> |
| <footnotes> |
| | <footnote id="F1"> Represents vesting of 100% of the time-based restricted share units granted on May 8, 2018. </footnote> |
| | <footnote id="F2"> Grant of restricted share units that vest 100% one year from date of grant. </footnote> |
| | </footnotes> |
| <remarks></remarks> |
| <ownerSignature> |
| | <signatureName> /s/ James F. Palmer </signatureName> |
| | <signatureDate> 2019-05-10 </signatureDate> |
| | </ownerSignature> |
| </ownershipDocument> |