Brand new 24V 500 mA center tap AC transformer.
Input is 110V/220V.  Output is 12V + 12V.

It measures W 42mm (67mm with the mounting tabs) D 40mm H 35mm

You get 24V by using the two blue wires only.  Black would not be used.
If you need 12V you can use one blue and one black wire.  Any of the blue can do.

This is an AC transformer and the output is AC also.
If you need DC you need a power supply not a transformer.
If you try to measure the output using the DC setting in your meter it would not give you a voltage.
You need to set it to AC in order to measure the output voltage.

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