The permission on usergroup level can be set to "unlimited" or to any number. On node level, the same permission can be set to values "inherit", "unlimited" or to a number. The general rule of permission override is the highest value wins. So, if you set "unlimited" on usergroup level, no matter what you set on node level, the value can not be overridden, and the final result will be "unlimited". If you set thread count to 10 in usergroups and set it to 5 in the node, 10 will be the final value used. If you set 0 in usergroups, and 5 in the node, 5 will be the final value used.