Weaver scope bolts

Hi,
Over the years I have had about 5 weaver bolts, the ones with the BIG round nut, break off while sitting in my gun cabinet.
I go to get a rifle out to shoot, and upon inspection, see that the nut is gone , and the bolt is still in.
These are from the cheaper aluminum ones I have both the "hook" over ones and the newer 4 x 4 ones.
First off I only use these with 22-250 and smaller rifles or, rimfires, anything bigger I use grand slams or steel rings and bases, millet, Burris and Leopold.
Second, I know that I have over torqued theses, with such a large slot, I have to use a screw driver that fits it, and I over torque them.
To weavers credit, I explained the situation, and have received replacements free of charge. Good for Weaver, I appreciate that.
However, this spring, once again I found a nut laying on the floor of my gun cabinet, and sure enough, I found my 22 mag had the ring bolt broke off.
I like the 4x4 rings for economic reasons, I no longer use the hook style, they always twisted the scope when tightening, and was a pain in the rear, but I still want the use the 4x4's.
What size screw are these? I would like to get some stainless steel grade 8 bolts in this size and see what happens then.
Thanks in advance.