Hex insert's or nut sert's as we call them in trade are good fitting's..
These nut serts are as advertised, and arrived pretty quickly.. I have used these before, So I know they are good but are much harder to rivet in than the round one's because they are much thicker but once in the hole provided the hole is a tight fit on the sert it normally can't turn as you crimp it unlike the round one's.. Having the proper tool to crimp them in makes it an awful lot easier to put them in. But the round one's at least can be put in with just two spanner's but I have found it pays to damage the threads on the bolt after the sert so it doesn't turn as you crimp it up. But once crimped, and you undo the nut you can still undo the bolt, and if you wish change it for an un damaged one to finish the job...