I do not think this is an original spring bolt. It looks like there are 3 hash marks on the bolt that indicates it is a Grade 5 Bolt. This system was not in use when the Model A was manufactured.
"Maybe" they mean, DANGER, made in CHINA A Friend was slowly tightening a center bolt, after carefully stacking the leaves, on his '34 Pickup & found that it DIDN'T have enough threaded section---+*$&^$#$+=*#---Where did he lurn those wurds??? Bill Embarrased
So, what's the deal with the current suppliers center bolts? Their recommended lengths are about 2-3 inches too long. The nut bottoms out before it even sandwiches the leafs.