The answer is 2.5 cm or about 1 inch
We use solenoids when the process of machines involves linear and rotary motion. Solenoids are among one in many actuation devices in terms of cost, size, simplified installation and ease of use. In both pull and push type solenoid, the plunger is pushed into the solenoid coil when the coil is energized. Both have strokes of 2.5 cm or 1 inch.
