The standard, and the others
The touchproof DIN 42802 connector is the standard of modern neurophysiology. It is a 1.5 mm pin shrouded in an insulating body, so that no conductive part is reachable by finger when the plug is out of its socket. If your polygraph is less than fifteen years old, it is very probably this one.
The bare 1 mm and 0.7 mm plugs are older. They are still found on headboxes, on EMG needles and on short-lead adhesive electrodes. They look alike in the hand, and that is precisely the problem.
The snap stud carries no cable at all: the adhesive electrode carries a stud, and a separate reusable lead brings it to the equipment. It is the most economical option as soon as volume follows.
DIN 42802 touchproof
1.5 mm shrouded pin. The standard.
1 mm male plug
Bare. Needles and older electrodes.
0.7 mm male plug
Bare. Headboxes and pin adhesives.
Snap stud
Adhesive electrode, separate lead.
Key-type plug
Dedicated modules, older sensors.
5-pin DIN
Certain EMG amplifiers.
How to identify yours in thirty seconds
Take an electrode you already use and look at its equipment end. If the pin is sunk into a plastic body that extends past it, it is touchproof DIN 42802. If the metal pin is bare along its whole length, it is a 1 mm or 0.7 mm plug.
To tell those two apart, compare with a mechanical pencil lead: a standard lead is 0.7 mm. If the pin is the diameter of a lead, it is 0.7. If it is visibly thicker, it is 1 mm.
If the end is a round metal stud with no cable, it is a snap. If it is a metal cylinder with a side notch, it is a key-type plug. If it is a round connector with several pins, count them: five means 5-pin DIN.
If in doubt, photograph the end and send us the picture. We identify it and tell you which reference to order.
When an adapter is enough
A connector mismatch does not condemn a sensor. Half the cases are solved by an adapter costing a few euros: 2 mm plug to DIN 42802 and back, 2 and 4 mm sockets, crocodile clip for a tab electrode with no connector at all.
Two cases need an interface cable rather than a simple adapter, because there is electronics inside: the RIP inductance bands, which take one cable per channel, thorax or abdomen, and the key-plug thermistor, which the 1450B cable brings back to DIN 42802.
One case does not resolve: pin diameter. A 0.7 mm female damaged by a 1 mm plug cannot be repaired, and no adapter makes up for a widened contact.