They are 1.5" diameter and will be cooked in an oven at 350
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Here's a recipe that sounds somewhat similar to what you're trying to do that calls for baking 35 minutes @ 350: http://food52.com/recipes..."Perfection," though, will depend just as much on the prep as the cooking; hopefully you've incorporated some kind of fat if you're using 90% lean meat or leaner, and that the ingredients haven't been over mixed. Both can lead to dry or tough meatballs.
I found a food thermometer hiding in the back of a drawer, tested a meatball at 15 min and it was 155, looks like 17 min was the ideal goal