I don't think you should put this in the OnEquip section, since the OnEquip section is like a, Run 1 time, then stop area. Meaning, if it's on the OnEquip section and you equip it, your str will go to 50, but if you equip other items after that, it'd increase it as well. (Atleast I'm pretty sure that's what will happen).
However if you just put it in the normal script section, it'll do a sort of, (loop refresh) constantly making sure your str does what it's supposed to. Meaning any gear equipped later on, shouldn't affect it.