<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType><periodOfReport>2003-06-30</periodOfReport>
    <issuer>
        <issuerCik>0000091440</issuerCik>
        <issuerName>SNAP ON INC</issuerName>
        <issuerTradingSymbol>SNA</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId>
            <rptOwnerCik>0001205044</rptOwnerCik>
            <rptOwnerName>TEERLINK RICHARD F</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><nonDerivativeSecurity><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2003-06-30</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved><footnoteId id="F1"/></transactionCoding><transactionAmounts><transactionShares><value>86</value></transactionShares><transactionValue><value>29.03</value></transactionValue><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>12357.915</value><footnoteId id="F2"/><footnoteId id="F3"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeSecurity><footnotes><footnote id="F1">Payment of fees in stock under the Corporation's Directors' 1993 Fee Plan.</footnote><footnote id="F2">Includes 98.275 shares acquired in June 2003 under the Corporation's Dividend and Direct Stock Purchase Plan.</footnote><footnote id="F3">The reporting person also directly owns the following stock options to purchase shares of Snap-on Incorporated common stock: (i) 3,000 shares at $43.6875 per share (exercisable 4/24/98 and expiring 4/24/08); (ii) 3,000 shares at $31.938 per share (exercisable 4/23/99 and expiring 4/23/09); (iii) 3,000 shares at $26.4375 per share (exercisable 4/28/00 and expiring 4/28/10); (iv) 3,000 shares at $29.36 per share (exercisable 4/27/01 and expiring 4/27/11); (v) 3,000 shares at $32.08 per share (exercisable 4/25/02 and expiring 4/25/12); and (vi) 3,000 shares at $28.43 per share (exercisable 4/24/03 and expiring 4/24/13).</footnote></footnotes><ownerSignature><signatureName>Jason D. Bartel under Power of Attorney for Richard F. Teerlink</signatureName><signatureDate>2003-07-02</signatureDate></ownerSignature></ownershipDocument>

