Klein Tools MM300 Digital Manual-Ranging Multimeter

The Klein Tools MM300 is an entry-level manual-ranging digital multimeter carrying a CAT III 600V rating independently certified by ETL (Intertek certificate #5000573) to UL 61010-1 and CSA C22.2 standards — the same certification as the MM400, confirmed from the back-panel label. It is averaged-response (not True-RMS), meaning it delivers accurate readings on clean DC and standard sine-wave AC but underreads 10–15% on PWM signals found in modern motor controls and LED lighting drivers. The feature set covers AC/DC voltage up to 600V, AC/DC current up to 10A, resistance to 2 MΩ, continuity with audible beep, diode test, and battery test. No backlight, no auto-ranging, no capacitance or temperature. Community reception is strong at 4.7 stars across 1,614 Amazon ratings, with multiple reviewers confirming reliable performance after two-plus years of regular use.

A home mechanic or DIYer who primarily checks battery voltage, tests fuses and relays, and does basic 12V continuity work will find the MM300 accurate and properly certified for those tasks. The ETL Listed CAT III 600V rating is real — safe to probe household AC when needed. Skip it if you work in dim engine bays without a separate light source (no backlight), probe modern vehicles with PWM-heavy systems where an averaged-response meter gives wrong readings, or want to avoid manually selecting ranges for every test. The Klein Tools MM400 adds auto-ranging, a backlight, capacitance, frequency, and temperature at a modest step-up, and is the more capable choice if you work diagnostics regularly.

The MM300 carries an ETL Listed mark (Intertek certificate #5000573), certifying conformance to UL Std 61010-1, 61010-2-030, and 61010-2-033, and certification to CSA Std C22.2 #61010-1, 61010-2-030, and 61010-2-038 — ETL is an Intertek NRTL mark equivalent to UL Listing for independent laboratory accreditation purposes. No active CPSC recall is on file. Input protection specifics (HIC fuse ratings, MOV presence) are not independently documented for the MM300 — the ETL certification confirms the protection was tested to UL 61010-1 standards, but no teardown documentation of component-level details is available. Powered by a standard 9V alkaline battery (included); dispose via Call2Recycle or a participating retailer. The ABS housing is standard e-waste at end of life.