SPST vs SPDT vs DPDT and How to Read Contact Notation
SPST vs SPDT vs DPDT comes down to two numbers: how many circuits move, and how many destinations each one has. SPST moves one circuit on or off. SPDT moves one circuit between two destinations. DPDT moves two separate circuits between two destinations each. Swiclick is a switch manufacturer whose own catalogue uses both the Western letter codes and the numeric style common across Asian suppliers, sometimes within the same product family, so this page decodes both. The codes carry less information than most people assume.
SPST vs SPDT vs DPDT Comparison Table
| SPST | SPDT | DPDT | |
| Poles (circuits moved) | 1 | 1 | 2 |
| Throws (destinations each) | 1 | 2 | 2 |
| Typical terminals | 2 | 3 | 6 |
| Common terminal | None | One | One per pole |
| Open in either stable position | Yes when unactuated, on the NO variant | No, on a conventional two-position maintained changeover. Centre-off variants differ | Same as SPDT, per pole |
| Numeric equivalent | 1P1T | 1P2T | 2P2T or DP2T |
What this table does not answer: which one your circuit needs. That decision sits on the SPST switch, SPDT switch and DPDT switch pages.
Reading the Letters
The letters split into two halves and each half answers one question.
The first half counts poles. SP is single pole, DP is double pole, 3P is three pole. A pole is one electrically independent circuit that the mechanism moves. Two poles in one body share an actuator and nothing else.
The second half counts throws. ST is single throw, DT is double throw, 3T is three throw. A throw is one destination the pole can connect to. Single throw means on or off. Double throw means it goes to one place or the other.
That is the whole grammar. The pole and throw notation is consistent enough that any code translates, which is why a code you have not seen before is still readable. 3PDT is three independent circuits each moving between two destinations.
A Terminal Count Sanity Check
There is a quick check that catches a mismatch between a code and a part before you order.
Terminals = poles x (throws + 1)
The plus one is the common terminal each pole needs. Run it against the Swiclick catalogue and it holds: 1P2T gives three terminals, 2P2T gives six, a DP3T part gives eight, and a 4P2T panel mount body gives twelve. Single throw is the exception where no common is needed, so SPST gives two and DPST gives four.
Treat this as a sanity check rather than a rule. Illuminated switches, mechanical support pins, internally joined commons, shield terminals and other constructions all produce exceptions. A four-pin tact switch is usually still one circuit, with two pins joined internally on each side. If the pin count is higher than the check predicts, read the contact diagram before assuming you found an extra pole.
Why Your Datasheet Says 1P2T
Buyers working across suppliers meet the same configurations written two ways, and the Swiclick catalogue itself uses both.
| Letter code | Numeric code | Poles | Throws | Terminals |
| SPST | 1P1T | 1 | 1 | 2 |
| SPDT | 1P2T | 1 | 2 | 3 |
| DPST | 2P1T | 2 | 1 | 4 |
| DPDT | 2P2T, DP2T | 2 | 2 | 6 |
| DP3T | 2P3T | 2 | 3 | 8 |
| 3PDT | 3P2T | 3 | 2 | 9 |
| 4PDT | 4P2T | 4 | 2 | 12 |
Both systems describe the same thing. The numeric style is common through the slide switch range, where part names such as 1P2T, 2P2T, DP2T, DP3T and 4P2T appear alongside SPDT and DPDT on neighbouring products.
Two habits avoid the confusion this creates. Write the configuration both ways in an RFQ, because a supplier reading only one system will not query the other. And run the terminal count check, since a mismatch between the code and the pin count usually means one of them is a catalogue error.
Catalogue audit, July 2026: across 175 listed Swiclick models, 32 part numbers state a configuration code in the product name. Of those, 8 state SPST or 1P1T, 10 state SPDT or 1P2T, 9 state DPDT, 2P2T or DP2T, 4 state DP3T or 2P3T, 1 states 4P2T, and none state DPST or 2P1T. Counts are by listed part number at the review date and cover only models that name the configuration, so other parts carry these configurations without stating them. Figures may change as the catalogue is updated.
What the Code Does Not Cover
Five specifications sit outside the configuration entirely, and all five belong in an RFQ.
Resting state. Which throw is closed when nothing is actuating the switch. NO and NC carry this, the pole and throw code does not.
Momentary or maintained. Whether the switch returns when released. This is independent of the pole and throw code, and availability depends on the product family and part number.
Shorting or non-shorting. Whether the common touches both throws during transition. It matters whenever the throws are separate sources.
Ratings and load type. The code carries no electrical information at all.
Terminal numbering. Which physical pin is which. This is the most common cause of a mirrored assembly, and it varies between suppliers who both use the same code.
The configuration code is a starting point for a conversation, not a specification. What a part is actually approved for comes from the applicable certification scheme against the exact model.
FAQ
SPST moves one circuit on or off. SPDT moves one circuit between two destinations. DPDT moves two separate circuits between two destinations each.
Yes. 1P2T counts poles and throws numerically, SPDT spells them out. They describe the same configuration.
For multi-throw switches, a common sanity check is poles multiplied by the quantity of throws plus one, written as terminals = poles x (throws + 1). Single-throw switches use two terminals per pole. Extra pins are sometimes mechanical anchoring rather than circuit terminals.
Double pole triple throw. Two independent circuits, each able to reach three destinations, normally on eight terminals.
No. Momentary or maintained action is independent of the pole and throw code, and which is available depends on the product family and part number.
Regional convention. Letter codes are usual in Western catalogues and numeric codes across many Asian suppliers. Writing both into an RFQ removes the ambiguity.
Talk to an engineer
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Written by Eric Chen, Application Engineer, Swiclick.
