[DonRotolo]

With that solenoid actuator, the rod is extended normally. When you connect 12 volts DC to it, it should pull in about 3/4" with about 4 oz of force.

As you have discovered, when that doesn't happen, there's something wrong.

First thing I would try is make sure you really have 12 volts. Verify it somehow. Then I would try the wires the other way around. Normally a solenoid is not polarity-sensitive, but it is worth a try.

Last, measure the resistance of the solenoid. I am guessing that a 3.5 Watt 12 V solenoid would have a resistance of maybe 4 Ohms or so. If it is not even close to that, it may be faulty.

If you have 12 volts and it doesn't move with the wires connected one way or the other, call McMaster and see about getting a replacement.