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AMD K7 Athlon (Socket A version)
On top of the CPU small metall contacts can be found labeled L1 .. L7.

These contacts are used to determine voltage, front side bus (FSB) and multiplier.
Some CPU's have all contacts (bridges) intact and therefore can be forced by BIOS for different settings.
All other versions can be set "free select" mode by reconnecting the bridges. Reports indicate that even a pencil can do the job. Best would be a conductive silver pen. Many mainboard manufacturers provide a sticker with preprinted bridges to fix the contacts.

If your mainboard does not allow to select CPU settings you can set these by cutting appropriate contacts. See following tables:

CPU Marking Week of manufacturing Most probable overclocking
Duron 600
AKAA0022MPMW <22 800-850MHz
multiplier unlocked !
AKAA0024DPBW 24 800-850MHz
multiplier unlocked !
AKAA0027BPAW 27 900-950MHz
AKBA0029TPAW 29 900-950MHz
AKBA0029XPDW 29 850-900MHz
AKBA0029XPCW 29 950-1000MHz
AKBA0030EPIW 30 850-900MHz
AKBA0030EPGW 30 850-900MHz
AKBA0030RPAW 30 850-900MHz
AKBA0032EPAW 32 900-950MHz
AKBA0035CPAW 35 1000MHz
AKBA0036APAW 36 1000-1050MHz
AKBA0036APBW 36 950-1000MHz
AKBA0036BPHW 36 1000MHz
Duron 650
AKBA0026DPCW 26 900-950MHz
AKBA0031UPCW 31 1050-1100MHz
AKBA0032APEW 32 950-1000MHz
AKBA0038DPJW 38 1000-1050MHz
AKCA0043UPCW 43 900-950MHz
AKCA0043XPGW 43 950MHz
AKCA0045UPJW 45 850-900MHz
AKCA0045BPAW 45 900-950MHz
Duron 700
AKBA0038FPBW 38 1000-1050MHz
AKCAR0048XPMW 48 950-1000MHz
AKCA0049MPMW 49 900-950MHz
AKCA0049UPMW 49 900-950MHz
AKCA0101SPAW 01/2001 900MHz
AKCA0103MPMW 03/2001 950MHz
AKCA0105SPAW 05/2001 950MHz
Duron 750
AKBA0040TPHW 40 900-950MHz
AKCA0044TPFW 44 950MHz
AKCA0047SPNW 47 900-950MHz
AMCA0051CPAW 51 900-950MHz
AMCA0051TPAW 51 950MHz
AMCA0101FPAW 01/2001 900-950MHz
Duron 800
AKBA0037EPCW 37 1000-1050MHz
AKCA0046MPMW 46 950MHz
AKCA0051MPMW 51 950MHz
AKCA0104WPEW 04/2001 950-1000MHz
Duron 850
AKCA0051MPMW 51 1000-1050MHz