Last I checked, Fidelity truncates to 10 characters, but silently converts them all to digits. They map them all to their equivalents on a typical phone keypad... so it's not even using all the digits. Talk about awful security...

Edit to add: It appears they may have fixed this misfeature. I did personally verify that you could log into their website with the phone-equivalent digits at one point, maybe a year or two ago. There's also a few forum threads about it around the net, eg https://www.bogleheads.org/forum/viewtopic.php?t=93792#p1350...