I am not using screws on these. I use them on my rocking chairs because of the added stress from rocking. I don't use them on my stools, and only use them in certain situations on chairs. The front legs on these chairs are similar to my stools, and the joint is plenty strong to last for generations without the screw. The back leg has the added support from the two rails forming the back rest that sit into 3/4" deep mortises. Without that bottom rail adding support so close to the back leg joint, I would use 3" #14 screws to add support.