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Klein Tools MM420 Auto-Ranging True RMS Digital Multimeter (600V)

A 4,000-count auto-ranging True RMS multimeter rated CAT III 600V that measures up to 600 V and 10 A, plus temperature, capacitance, frequency and duty cycle.

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Klein Tools MM420 auto-ranging True RMS digital multimeter, front view
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Key facts

DC voltage
400 mV to 600 V; ±(0.5% + 5) on the 400 mV to 40 V ranges, ±(0.8% + 3) on 400 V, ±(1.0% + 3) on 600 V
AC voltage (True RMS)
4 V to 600 V, 50 to 400 Hz; ±(1.0% + 3) on 4 to 400 V, ±(1.2% + 5) on 600 V
DC current
400 µA to 10 A; ±(1.0% + 5) up to 400 mA, ±(2.0% + 5) on 4 A and 10 A
AC current
400 µA to 10 A; ±(1.0% + 5) up to 400 mA, ±(2.0% + 3) on 4 A, ±(2.0% + 5) on 10 A
Resistance
400 Ω to 50 MΩ; ±(1.2% + 5) up to 4 MΩ
Capacitance
40 nF to 400 µF
Frequency
Up to 50 kHz, ±(1.0% + 5)

Which version should you buy?

This page covers: MM420 meter with standard accessories.

  • MM420 meter with standard accessories

    This page

    Model: MM420

    What differs
    Auto-ranging True RMS meter supplied with leads, a thermocouple and batteries.
    Best for
    Electrical checks that need automatic ranging and temperature measurement.
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  • MM400 older meter

    Model: MM400

    What differs
    Discontinued predecessor with automatic ranging and a 1 m drop rating.
    Best for
    Replacing an existing MM400 with the same model.

  • 69149P basic test kit

    Model: 69149P

    What differs
    Contains an MM320 manual-ranging meter, NCVT1P pen and RT110 outlet tester.
    Best for
    Starting with a meter, voltage pen and basic outlet tester together.

  • 69355 test kit with LCD outlet tester

    Model: 69355

    What differs
    Contains an MM320 manual-ranging meter, NCVT3P pen with flashlight and RT250 LCD outlet tester.
    Best for
    A starter set that also checks GFCI trip time and detects low AC voltage.

Watch out

  • MM400 is the discontinued predecessor; check for MM420 on the meter.
  • The 69149P and 69355 kits contain MM320, not MM420.
  • The standard MM420 package includes leads and a thermocouple; a magnetic hanger is an added accessory.

Why people pick it

  • True RMS and auto-ranging, so mixed AC loads and quick checks need no range-hunting
  • Lead-Alert LEDs light the correct input jacks for the selected function
  • Adds temperature, capacitance, frequency and duty cycle to the basics
  • Rated for a 2 m drop

Know before you buy

  • Rated CAT III 600V: not for service-entrance (CAT IV) work
  • 4,000-count display, against 6,000 counts on Fluke's 107 and 117
  • Klein lists no low-impedance (LoZ) mode or built-in non-contact voltage detection
  • Accuracy is quoted per range: ±(0.5% + 5) at best on DC volts

Full specifications

DC voltage400 mV to 600 V; ±(0.5% + 5) on the 400 mV to 40 V ranges, ±(0.8% + 3) on 400 V, ±(1.0% + 3) on 600 V
AC voltage (True RMS)4 V to 600 V, 50 to 400 Hz; ±(1.0% + 3) on 4 to 400 V, ±(1.2% + 5) on 600 V
DC current400 µA to 10 A; ±(1.0% + 5) up to 400 mA, ±(2.0% + 5) on 4 A and 10 A
AC current400 µA to 10 A; ±(1.0% + 5) up to 400 mA, ±(2.0% + 3) on 4 A, ±(2.0% + 5) on 10 A
Resistance400 Ω to 50 MΩ; ±(1.2% + 5) up to 4 MΩ
Capacitance40 nF to 400 µF
FrequencyUp to 50 kHz, ±(1.0% + 5)
Duty cycle1.0% to 99.9%
Temperature-40 to 1832°F (-40 to 1000°C); the included K-type thermocouple is rated below 356°F (180°C) only, so hotter readings need a suitably rated probe
Continuity and diodeBeeps below 50 Ω; diode test
Display3¾-digit, 4,000-count backlit LCD
Input impedance10 MΩ
Fuses500 mA/600 V and 10 A/600 V fast-blow
FeaturesLead-Alert LEDs show which jacks to use; auto-ranging; Min/Max; data hold; auto power-off
Safety ratingCAT III 600V, Class 2, double insulation
Safety standardsConforms to UL 61010-1, 61010-2-030 and 61010-2-033; certified to CSA C22.2 No. 61010-1 and to IEC EN 61010-1
CalibrationAccurate for one year (per the manual)
Drop protection2 m (6.6 ft)
Power2 × AAA
Size162.7 × 79.4 × 46.6 mm (6.41 × 3.13 × 1.83 in), per the manual
Weight250 g (8.8 oz)
In the boxMeter, test leads with CAT III/CAT IV safety caps, thermocouple, 2 × AAA batteries, instructions

From manufacturer documentation, checked November 2, 2026. Spotted an error? Tell us.

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