I do not think it matters the plastic disc may be to keep beater fro mixing bowel. i would try it and see what happens, you could switch holes after trying it.
Instructions say to "press" (push in) the head tilt button. If the button wont move, try moving head up and down while applying pressure to the button.
Check on eBay. Sometimes you will find replacements--even new ones. You'll need the actual Model Number off the tag on your mixer (see link where to find that info).
Search Now for Replacement Parts Accessories HamiltonBeach com
Then search for:
Make Model replacement parts
If mixer is locked in down position, and you hear motor running, the problem could be worn gears in mixer head. Check warranty and return to place of purchase or take to small appliance repair shop for estimate.
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