And here are photos of Ken's hooks on my bucket. In the center is Ken's latest-and-greatest clevis fixture which I used to attach a 3/8" slip hook in the center of the bucket. It is helpful that the slip hook can be flopped over to the rear, moving it out of the way. This clevis fixture is new. I bolted it on the bucket over the weekend and have not hooked a load with it yet.
Presumably most tractor owners know that 5/16" grab hooks will "grab" 1/4" + 5/16" + 3/8" chain successfully, making the 5/16" sort of the universal size for all but the largest categories of tractors. If your tractor has Category 2=1" 3-pt hitch and you usually use 3/8" and sometimes 1/2" chain you might want larger grab hooks. But man, even 3/8" chain is heavy to work with through an afternoon.
Compact tractors loose tire traction before they can stress a 5/16" chain, so consider carefully before buying heavier chain. I use 1/4" chain, and Ken's grab hooks, only to roll-out 1"-2" saplings with their roots intact and vines from the ground with the bucket. The smaller vegetation is gripped by 1/4" chain while 5/16" chain will slip on dinky stuff. Except for small saplings and vines 5/16" chain is my default choice.
Tractor/Loader is a Kubota B3300SU.