5PCS DC 12V 4mm Stroke Mini Push-Pull Type Solenoid Micro DC Solenoid Electromagnet Electric Magnet Valve Open Frame Spring Solenoid Valves Linear Motion

Update: Turns out my 12v power supply was not working correctly and was only producing 5v. Using a different source these actuate just fine and work as described.These things are so weak they can't even overcome the springs that come installed on them. Do not buy, useless.

i expected to be more power ,so i can't use them

I expected this to work only with +voltage on the correct wire (which is not marked), but this thing seems to work with either polarity. which i like. but maybe i need to read the specs after i write this review!

These solenoids are so weak I wasn't able to measure them with a force gauge. They might have some useful application, but I can't think of what it would be.

The media could not be loaded.  The force of this solenoid is very low. It may work for you application, but it won't for me. As you can see in video, at around 12V the solenoid draws near the nominal current, but is easily dislodged by my finger with almost no effort. The force of the solenoid when it is fully extended will be even lower. Make sure your application requires almost no force before buying these.