Quick Answer:The Two Way Plug Key is a single-pole, double-throw plug selector with three brass blocks and two tapered plugs, used to connect a common terminal to either of two circuit branches, such as two cells whose EMFs are being compared.
Last updated: 18 October 2026
Key Features
Single-pole double-throw (SPDT) plug selector.
Three brass blocks with two gaps.
Two tapered brass plugs with insulated heads.
Switches a common terminal between two branches.
Technical Specifications
Specification
Value
Switch type
SPDT plug selector
Blocks
Three, high-conductivity brass
Gaps
Two
Plugs
Two, tapered brass with insulated moulded heads
How It Is Used
The common circuit is connected to the centre block and each branch to an outer block. Inserting one plug or the other routes the circuit to that branch, so a potentiometer can be balanced against one cell and then the other, or a bridge switched between known and unknown resistances.
Frequently Asked Questions
When is the Two Way Plug Key used?
When a circuit must be switched between two branches, for example comparing the EMFs of two cells on a potentiometer or swapping known and unknown resistances.
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