Klein MM600 Multimeter: What It Measures, How to Use It Safely, and What to Check First

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The Klein MM600 is an auto-ranging digital multimeter from Klein Tools. It measures AC and DC voltage, AC and DC current, and resistance, and the manufacturer’s manual also lists temperature, capacitance, frequency, duty cycle, diode test and audible continuity. This guide explains what the meter does, how to use it safely, which ratings the manufacturer publishes, and what to check before you buy a unit that may be second-hand or old stock.

Quick answer

The MM600 is an auto-ranging meter: you select the function, and the meter picks the measuring range.
Klein publishes a safety rating of CAT IV 600V and CAT III 1000V, with double insulation and a Class 2 rating.
The discontinued status matters for buyers. Check the seller and the packaging date before buying.
Read the manual’s safety section before you connect the leads to any live circuit.

What the Klein MM600 measures

According to the Klein instruction manual, the MM600 has these functions:

AC voltage up to 1000V AC, and DC voltage up to 1000V DC.
AC and DC current, with a 400mA setting and a 10A setting.
Resistance from 400.0 ohms up to 40.00 megohms.
Capacitance, frequency, duty cycle, temperature, diode test and audible continuity.

The display is a 4000-count LCD. The manual lists the auto-ranging behaviour for each function, so you do not need to choose a range manually for most measurements. You still need to choose the correct function on the dial before you connect the leads.

Ratings the manufacturer publishes

The manufacturer’s product pages and manual agree on the main ratings:

Safety rating: CAT IV 600V, CAT III 1000V, Class 2, double insulation. Pollution degree 2.
Maximum input: 1000V AC RMS or 1000V DC on voltage; 600V DC or AC RMS on resistance, capacitance, frequency and temperature.
Current fuses: the manual lists overload protection of 500mA/1000V and 10A/1000V.
Drop protection: 6.6 ft (2 m).
Ingress protection: IP42, except the test lead jacks, according to the manual’s warnings.
Power: two AAA batteries, as stated on the product page.
Operating conditions: -10 to 50 C (14 to 122 F), altitude up to 2000 m, humidity below 90 percent non-condensing.

The manual states the CAT categories in its own words. CAT III applies to circuits connected to the distribution part of a building’s low-voltage mains installation. CAT IV applies at the source of that installation. A CAT rating tells you the meter is designed for that environment. It does not make any task on live mains safe.

Accuracy as printed

The manual gives accuracy as a percentage of reading plus a number of least significant digits. For example, DC voltage on the 4V range is listed at plus or minus 1.0 percent plus 3 digits, and AC voltage on the 400V range at plus or minus 1.5 percent plus 5 digits. Accuracy is specified at 18 to 28 C. Outside that range the manual asks for a temperature correction of 0.1 times the quoted accuracy for each degree.

Read the accuracy table for the function you use. A figure for one range does not apply to another.

How to use it safely

Electrical work can kill. Before you measure anything on a mains circuit, follow these steps from the manual’s safety approach:

Read the manual’s warnings and the CAT rating section. Match the meter’s category to the circuit you plan to test.
Inspect the test leads and the meter case for cracks or exposed metal. Do not use damaged leads.
Set the function dial before you connect the leads, and keep your fingers behind the probe guards.
For current, the manual says the meter must be connected in series, and the 10A setting has its own maximum. Do not connect the probes across a voltage source while the dial is on a current setting.
Stop if the display does not respond as expected, and check the fuses and batteries before you go further.

Work on panels, service entrances and fixed mains wiring belongs with a licensed electrician. A handheld meter is a test tool, not a substitute for the training and equipment that job needs.

Beginner tasks the MM600 suits

The MM600’s function list fits common home and car checks:

Battery voltage: set DC voltage and measure the terminals of a small battery. Low-voltage DC is much less hazardous than mains, but a short across a large battery can still cause burns.
Continuity and diode checks: use the audible continuity and diode functions on a de-energized circuit or component.
Resistance: measure only on a circuit that is de-energized and isolated.

Check these before you buy

Klein’s product page states that the MM600 is “no longer in production.” That matters for three reasons:

A new unit may be old stock. Check the packaging date and the seller’s return policy.
Replacement parts and any future calibration may be harder to find. The manual says the meter is accurate for one year.
Klein’s pages point to a newer model. If you are buying for regular mains work, compare the current model’s ratings against the MM600 figures above before you decide.

Also check that the unit you receive has the same CAT rating, the same fuse ratings in the manual, and the same accessories. The product page lists a carrying case, test leads, a thermocouple, batteries and the manual, but the seller’s listing may differ.

How we chose

This guide uses only the figures in three Klein Tools sources: the manufacturer’s US product page, the Klein UK product page, and the MM600 instruction manual, all opened on 2026-10-27. We did not compare the MM600 with other meters in this guide. The sources do not rank the meter against competitors, so this article does not either.

What we could not verify

The sources we opened do not state whether the MM600 is true RMS. Check the manual’s wording for AC measurement before you rely on it for non-sinusoidal signals. The sources also do not give the current price, stock level or the newer model’s exact ratings, so check those with Klein and the seller directly.

Where to go next

If you are choosing a first meter, read our guide to auto-ranging multimeters to see how auto-ranging compares with manual ranging. For a broader buying guide, see true RMS multimeters, which explains when true RMS matters. For home use, our home-use multimeter guide covers the common outlet, battery and continuity checks.

Buying checklist

Confirm the CAT rating printed on the meter matches the manual.
Check the fuse ratings and whether replacement fuses are available.
Check the packaging date and the seller’s return policy, given the discontinued status.
Confirm the included leads and accessories against the product page.
Read the manual before first use.

Mistakes to avoid

Choosing a meter for mains work without checking its CAT rating against the circuit.
Using the 10A current setting on a circuit whose current you have not estimated.
Assuming an auto-ranging meter is safer than a manual one. Auto-ranging changes the range, not the safety rating.
Measuring resistance or continuity on a live circuit.

FAQ

Is the Klein MM600 auto-ranging?

Yes. The manual describes the meter as an automatically ranging digital multimeter, so you choose the function and the meter selects the range.

What is the CAT rating of the MM600?

Klein publishes CAT IV 600V and CAT III 1000V, Class 2, double insulation.

Is the MM600 still made?

Klein’s product page says the MM600 is no longer in production. Confirm this with the seller before buying.

What batteries does it use?

The product page lists two AAA batteries.

Does the MM600 measure temperature?

Yes. The manual lists a range of 0 to 1000 F (-18 to 538 C) with a resolution of 0.1 F or 0.1 C on the lower ranges.

What is the drop rating?

The manual gives a drop protection rating of 6.6 ft (2 m).

Bottom line

The Klein MM600 is a documented auto-ranging meter with a published CAT IV 600V and CAT III 1000V rating. Match that rating to the circuit you test, read the manual before use, and check the discontinued status before you buy.

Sources

Klein Tools, “Digital Multimeter, Auto-Ranging, 1000V” product page, https://kleintools.com/product/MM600 (opened 2026-10-27)
Klein Tools UK, MM600 product page, https://www.kleintools.co.uk/product/MM600 (opened 2026-10-27)
Klein Tools, MM600 Instruction Manual (PDF), https://data.kleintools.com/sites/all/product_assets/documents/instructions/klein/MM600_1390111ART_WEB.pdf (opened 2026-10-27)

Klein Mm600