Quarter-inch drive is the small-fastener range: interior trim, electrical, brackets, sensors and anything where a bigger ratchet simply will not fit. This is the complete list of 12 six-point metric regular sockets, with the Teng part number for each.
What quarter-inch drive is for
The square drive is the weakest link in any socket assembly, and a quarter-inch square is deliberately the weakest of the common sizes. That is a feature. Working on 5 to 13 mm fasteners in thin brackets, plastic housings and alloy castings, the thing most likely to fail is the fastener or the thread it sits in, not the tool — so a drive that gives up before the casting does is a useful ceiling. Treat roughly 25 Nm as the working limit and step up to 3/8 inch drive above it rather than reaching for a longer handle.
Feel matters more here than anywhere else
Small fasteners give very little warning before they strip. The difference between a 6 mm bolt correctly tightened and the same bolt with its thread pulled is a few degrees of rotation, and the only signal is the change in resistance travelling up through the tool. That is the argument for a short ratchet and a properly fitting six-point socket rather than a long handle and a twelve-point: everything that adds leverage or flex between your hand and the hex removes the feedback you are relying on.
All 12 sizes
| Size | Decimal inch | Teng part number | EAN |
|---|---|---|---|
| 4 mm | 0.1575 | M140504-C | 5020385130067 |
| 4.5 mm | 0.1772 | M1405045-C | 5020385132085 |
| 5 mm | 0.1969 | M140505-C | 5020385130074 |
| 5.5 mm | 0.2165 | M1405055-C | 5020385130081 |
| 6 mm | 0.2362 | M140506-C | 5020385130098 |
| 7 mm | 0.2756 | M140507-C | 5020385130104 |
| 8 mm | 0.3150 | M140508-C | 5020385130111 |
| 9 mm | 0.3543 | M140509-C | 5020385131033 |
| 10 mm | 0.3937 | M140510-C | 5020385130128 |
| 11 mm | 0.4331 | M140511-C | 5020385130135 |
| 12 mm | 0.4724 | M140512-C | 5020385130142 |
| 13 mm | 0.5118 | M140513-C | 5020385130159 |
Where this list comes from
Every row is read from the live Teng Tools USA catalogue on the day this page was generated — product record, part number and size taken from the record itself, never transcribed from a printed catalogue or inferred from a pattern. Sizes are the across-flats dimension in millimetres. The 5.5 mm size is genuinely part of the range rather than a typo — it is common on European electrical hardware. A size that has been discontinued disappears from this list rather than lingering as a part number you cannot order, which is the failure mode of every static spec sheet. Decimal inch equivalents are exact conversions at 25.4 mm to the inch, rounded for display only. They are given for cross-referencing against an imperial drawing, not as a claim that a metric socket fits an imperial fastener — it does not.
The half-millimetre sizes
Metric ranges include 5.5 mm and, in some families, other half sizes. They are not rounding artefacts: 5.5 mm hex heads are standard on hose clips, battery terminals and a great deal of German electrical hardware. Forcing a 6 mm socket onto one works precisely once, and afterwards neither the fastener nor the next attempt is in good shape. If a small hex feels loose in a 6 mm socket, the answer is usually 5.5 rather than a firmer grip.
The range is in sockets and accessories, and complete ranges in socket sets.