A deep socket exists for one reason: to reach a nut that sits partway down a stud. This is the complete list of 16 deep six-point metric sockets in 3/8 inch drive, with the Teng part number for each size.
When depth is the whole job
A regular socket bottoms out on the end of a protruding stud long before it reaches the nut. U-bolts, exhaust studs, shock mounts, battery clamps and almost anything on a bracket that was designed to be adjustable share that geometry. A deep socket clears the stud inside its own bore and grips the nut properly rather than gripping the top two millimetres of it. Trying to do that job with a regular socket and an extension bar does not help — the bar adds reach behind the socket, not inside it.
The cost of using deep sockets by default
Depth is not free. A deep socket puts the ratchet head further from the fastener, and that distance multiplies any sideways force into a rocking motion at the hex. It also takes more room above the fastener than many engine bays have, and the extra length flexes fractionally under high torque, which blunts the feel that tells you a fastener is about to yield. Reach for regular first and go deep when the fastener needs it — the reverse habit rounds nuts on shallow studs.
All 16 deep sizes
| Size | Decimal inch | Teng part number | EAN |
|---|---|---|---|
| 7 mm | 0.2756 | M380607-C | 5020385132818 |
| 8 mm | 0.3150 | M380608-C | 5020385130463 |
| 9 mm | 0.3543 | M380609-C | 5020385132825 |
| 10 mm | 0.3937 | M380610-C | 5020385130470 |
| 11 mm | 0.4331 | M380611-C | 5020385130845 |
| 12 mm | 0.4724 | M380612-C | 5020385130487 |
| 13 mm | 0.5118 | M380613-C | 5020385130494 |
| 14 mm | 0.5512 | M380614-C | 5020385130852 |
| 15 mm | 0.5906 | M380615-C | 5020385130869 |
| 16 mm | 0.6299 | M380616-C | 5020385130876 |
| 17 mm | 0.6693 | M380617-C | 5020385130500 |
| 18 mm | 0.7087 | M380618-C | 5020385132832 |
| 19 mm | 0.7480 | M380619-C | 5020385130517 |
| 20 mm | 0.7874 | M380620-C | 5020385132849 |
| 21 mm | 0.8268 | M380621-C | 5020385132856 |
| 22 mm | 0.8661 | M380622-C | 5020385132863 |
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. Deep and regular sockets in the same size are different part numbers and are listed separately. 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.
Deep sockets and impact tools
These are chrome sockets for hand and ratchet use. A deep chrome socket on a rattle gun is the single most common way one gets destroyed: the hardened, brittle chrome finish that gives a hand socket its thin walls and clean fit does not absorb the hammer blows an impact wrench delivers, and the longer body gives the shock more length to work on. Anything driven by an impact wrench needs a socket built for it.
Impact-rated equivalents are in impact sockets; the chrome range is in sockets and accessories.