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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2024-10-22</periodOfReport>

    <issuer>
        <issuerCik>0000105132</issuerCik>
        <issuerName>WD 40 CO</issuerName>
        <issuerTradingSymbol>WDFC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001691913</rptOwnerCik>
            <rptOwnerName>Brass Steven A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O:  WD-40 COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>9715 BUSINESSPARK AVE.</rptOwnerStreet2>
            <rptOwnerCity>SAN DIEGO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92131</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>true</isDirector>
            <isOfficer>true</isOfficer>
            <officerTitle>President and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>false</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2024-10-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1672</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>27361</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2024-10-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1058</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>26303</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2024-10-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>253</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>26050</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares withheld pursuant to mandatory provisions of Restricted Stock Unit (RSU) Award Agreement(s) in satisfaction of tax withholding obligations upon vesting of 3,296 RSUs.</footnote>
        <footnote id="F2">Shares withheld pursuant to mandatory provisions of Market Share Unit (MSU) Award Agreement in satisfaction of tax withholding obligations upon vesting of 2,086 MSUs.</footnote>
        <footnote id="F3">Shares withheld pursuant to mandatory provisions of Performance Stock Unit (PSU) Award Agreement in satisfaction of tax withholding obligations upon vesting of 498 PSUs.</footnote>
        <footnote id="F4">Total includes:  (i) 10,091 unvested RSUs, (ii) 1,218 shares of restricted Common Stock received upon settlement of PSUs, (iii) 108 vested deferred performance units or DPUs, which are Common Stock equivalents, and (iv) 2,224 shares held in Reporting Person's WD-40 Company Profit Sharing / 401(k) Plan account.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Ann T. Nguyen, attorney-in-fact for Steven A. Brass</signatureName>
        <signatureDate>2024-10-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0508
4
2024-10-22
0000105132
WD 40 CO
WDFC
0001691913
Brass Steven A
C/O:  WD-40 COMPANY
9715 BUSINESSPARK AVE.
SAN DIEGO
CA
92131
true
true
President and CEO
false
Common Stock
2024-10-22
4
F
0
1672
D
27361
D
Common Stock
2024-10-22
4
F
0
1058
D
26303
D
Common Stock
2024-10-22
4
F
0
253
D
26050
D
Shares withheld pursuant to mandatory provisions of Restricted Stock Unit (RSU) Award Agreement(s) in satisfaction of tax withholding obligations upon vesting of 3,296 RSUs.
Shares withheld pursuant to mandatory provisions of Market Share Unit (MSU) Award Agreement in satisfaction of tax withholding obligations upon vesting of 2,086 MSUs.
Shares withheld pursuant to mandatory provisions of Performance Stock Unit (PSU) Award Agreement in satisfaction of tax withholding obligations upon vesting of 498 PSUs.
Total includes:  (i) 10,091 unvested RSUs, (ii) 1,218 shares of restricted Common Stock received upon settlement of PSUs, (iii) 108 vested deferred performance units or DPUs, which are Common Stock equivalents, and (iv) 2,224 shares held in Reporting Person's WD-40 Company Profit Sharing / 401(k) Plan account.
Ann T. Nguyen, attorney-in-fact for Steven A. Brass
2024-10-23