Lever Handle Kit

The set screw was pretty much stripped when removing it, trying to repair a leak. I want to replace it before it is too late and so just need the item number for it and not the whole handle assembly?... Also, what size hex bit/allen key is supposed to be used to remove the set screw?... as i could not find a very good fit with any of the sets I tried, which likely contributed to the issue. That part doesn't seem the best made. Please let me know ASAP. Thanks!