Squirrel BusterClassic Squirrel-proof Bird Feeder w/4 Feeding Ports, 2.4-pound Seed Capacity

Can large birds feed as well? I have a flock of grackles that will clean out my feeder in a day. Will they close the feeder as well?

How often should I clean my Brome 1015-V01 birdfeeder?

I have a SquirrelBuster Classic that appears to be fine but the Bolt on the bottom is missing. How can we purchase a new Bolt?? Size is 20" with the pointed top on; 16" plastic clear tube; green cage is 4" across.

Does this feeder have to be hung on a pole? If I hang it off the deck with a short hook, will squirrels still reach into the ports?