Finally got my answer to that question today!
Initially I had gone to Home Depot to find a 2mm or 3mm metric screw. The guy there had a template, but still couldn't tell me what size to look for. Home Depot in my area does not sell metric screws less than 4mm.
I finally got a chance to visit Ace Hardware today. Not only were they able to use a template to tell me what size screw to get, but had quite a few in stock for 37 cents! I bought 3 just in case.
The metal metric screw size you need to replace the plastic screw on your Pazzles Inspiration Pen Tool screw is 3mm. There are different lengths, but thank goodness there was only two lengths I had to choose from or I may have been in trouble. Actually, what helped me determine the length was the fact that I had the plastic screw and the pen tool with me. I had the guy screw in the metal screws to the pen tool to make sure they fit.
Yayyy! I also tested when I got home with a #2 pencil. Works really well. I got lucky and put the pencil in just right for the PI to correctly print for me. The first two fonts, some of the letters were not closed all the way so I tried a different font and it closed all letters like it should. I know for sure I will be using the pen tool a lot!
I hope this information helps you.