Dug around in the shop and found a stock bolt and here's the driver, too. If you are going to mess much with Lee's a purpose-built screwdriver is pretty handy to have around.

By the way, IIRC, stocks vary in what length of bolt they will take. I seem to remember the shoulder on some stocks was at somewhat different depth than others. I can't remember if a standard bolt WOULDN'T work, but do seem to remember that different lengths of bolts WOULD work, if that makes sense.