UK What M8 and M12 connectors are
M8 and M12 are screw-locking circular connectors used on sensors, actuators, field devices and rugged computers. The number is the metric thread on the coupling nut: M8 has an 8 mm thread and M12 a 12 mm thread. Both screw together by hand and seal to IP67 or better when mated, so they keep dust, water and vibration out of the joint.
The difference is size and capacity. M8 saves space on small sensors and light grids, where the connector body can be no bigger than the device. M12 has room for more pins, larger contacts and the twisted pairs that Ethernet needs, so it has become the standard sealed connector for anything carrying real power or network data.
M8 is defined mainly in IEC 61076-2-104 and M12 in the IEC 61076-2-101, -109 and -111 family, which also sets the M12 codings.
M8 vs M12 at a glance
The ratings below are typical values for standard connectors. Exact figures depend on the pin count, coding and manufacturer.
| Feature | M8 | M12 |
|---|---|---|
| Thread | M8 × 0.5, 8 mm | M12 × 1, 12 mm |
| Pin counts | 3, 4, 6 or 8 | 3 to 12, plus power and Ethernet layouts |
| Typical current | Around 3 to 4 A on 3 or 4 pins, less on 8 | Around 4 A on signal codings, up to 16 A on power codings |
| Ethernet | 4-pin, up to 100 Mbit/s | D-coded 100 Mbit/s, X-coded up to 10 Gbit/s |
| Codings | A, B and D, plus snap-in versions | A, B, C, D, X and L, T, S, K power codings |
| Locking | Screw or snap-in | Screw, with push-pull options |
| Sealing | IP67 when mated | IP67, with IP68 and IP69K versions |
| Typical use | Small sensors, encoders, light grids | Sensors, Ethernet, power, computers |
Coding is the bigger story on M12. With nine codings to choose from, the same thread carries a sensor signal, a 10 Gbit/s network link or a 16 A supply. Our M12 coding explainer shows how the key on each one stops the wrong cable being fitted.
When to use M8
M8 is the right connector where space on the device is the constraint and the signal is light. Typical examples are:
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Miniature sensors. Inductive proximity sensors, photoelectric sensors and small reed switches often have an M8 pigtail or socket.
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Valve and actuator heads. Low-current coils and position feedback fit easily on 3 or 4 pins.
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Compact cameras and encoders. Some machine vision cameras use M8 for trigger and I/O alongside a larger data connector.
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Dense I/O boxes. An M8 I/O block fits more ports into the same width than an M12 block.
When to use M12
Use M12 for everything that carries real power or network data. Its larger contacts handle more current, and the X-coded version carries Gigabit and 10 Gigabit Ethernet with a shield between each pair. M12 is also the usual connector for IO-Link, where a master port uses a 4- or 5-pin A-coded socket.
That is why rugged and waterproof computers standardise on M12 rather than M8. Our IP67 computers put Ethernet, serial, USB and DC power on sealed M12 sockets, and our M12 Ethernet switches do the same for the network. Our guide to M12 waterproof connectors covers the wider case for sealed connectors at the edge.
Ethernet and power on M8
M8 can carry Ethernet, but only at Fast Ethernet speeds. A 4-pin D-coded M8 connector, defined in IEC 61076-2-114, carries 100 Mbit/s over two pairs and is used on compact cameras, small switches and drives where an M12 socket will not fit. There is no M8 equivalent of X-coded M12, so any device that needs Gigabit Ethernet or faster moves up to M12.
Power follows the same pattern. M8 power versions exist for small motors and valve banks, but their current rating stays at a few amps, while the M12 power codings reach 16 A. A computer that draws tens of watts from a 24 V supply, with a start-up surge on top, is a job for M12. That size step is also why M12 is easier to service in the field: the larger nut is simpler to grip with gloves, and the larger contacts tolerate repeated mating better over the life of the installation.
Mixing M8 and M12 on one machine
Most machines use both: M8 at the small sensors and M12 at the I/O blocks, switches and computers. Adaptor cables with an M8 plug at one end and an M12 socket at the other join the two, provided the coding and pin count carry the same signals. Keep the tightening torque in mind too. M8 nuts are tightened lightly by hand, typically to around 0.2 to 0.4 Nm, while M12 nuts take around 0.4 to 0.6 Nm; overtightening an M8 nut is a common cause of a cracked housing.
Quick answers on M8 vs M12
M8 and M12 connectors: common questions
What does M8 or M12 mean?
The thread size. M8 has an 8 mm metric coupling thread and M12 a 12 mm thread. The number says nothing about pins, coding or speed.
Is M12 the same as 12 mm?
For the thread, yes. The coupling nut has a 12 mm metric thread. The connector body and cable are larger than that once the nut and overmould are added.
Can an M8 connector carry Ethernet?
Yes, at up to 100 Mbit/s. A 4-pin M8 Ethernet connector carries Fast Ethernet over two pairs. For Gigabit or faster, use X-coded M12.
Can I plug an M8 cable into an M12 socket?
Not directly. The threads differ, so you need an M8 to M12 adaptor cable with the right coding and pin count at each end.
Which is better, M8 or M12?
Neither in general. M8 is better where space is tight and the signal is light. M12 is better for power, Ethernet and anything that needs more than a few pins.
We supply our rugged and waterproof computers with M12 I/O as standard, and we match the coded cables and any M8 adaptors to your sensors before the system ships.