I just measured one - 2" long.
Just got a set of Marlin spikes from Opie. They were about 2.5" in length. I made some myself at about 2.75". The ones from Opie seemed a little on the short side, just my opinion.
I don't know if Opie has the "Keebler Elfs" working for him, but the keeper strings made from "Zingit" are awesome. You plan on doing something like that?