<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2023-12-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000098362</issuerCik>
        <issuerName>TIMKEN CO</issuerName>
        <issuerTradingSymbol>TKR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001508035</rptOwnerCik>
            <rptOwnerName>Coughlin Christopher A</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>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP &amp; Pres. Industrial Motion</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2023-12-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4285</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>79.97</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>89339</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents withholding on August 3, 2022 grant of deferred shares (previously reported) that vested on December 31, 2023.</footnote>
        <footnote id="F2">Includes 1,507 shares earned through dividend reinvestment in 2023.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Christopher A. Coughlin</signatureName>
        <signatureDate>2024-01-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0508
4
2023-12-31
0
0000098362
TIMKEN CO
TKR
0001508035
Coughlin Christopher A
4500 MT. PLEASANT ST. NW
NORTH CANTON
OH
44720
0
1
0
0
EVP & Pres. Industrial Motion
0
Common Stock
2023-12-31
4
F
0
4285
79.97
D
89339
D
Represents withholding on August 3, 2022 grant of deferred shares (previously reported) that vested on December 31, 2023.
Includes 1,507 shares earned through dividend reinvestment in 2023.
/s/ Christopher A. Coughlin
2024-01-03