Re: Acorn vs. Hex Nuts
OK I wasn't specific. THE CHINESE SUPPLIED BIKE KIT acorn nuts USED for the HEAD studs are a JUNK IDEA - Use them in your next concrete pour.
In and of themselves acorn nuts are not bad. They are just not what to use for any head stud, unless you leave some exposed stud thread and use them for decorative caps.
If you are interested in properly torquing your head nuts, throw away (or set aside!) the acorn nuts and use a proper torque wrench and good hex nuts.
So in closing, throw away the BIKE KIT acorn nuts. Use them in your next concrete pour. Following this is very sound advice and will prevent stripped studs. No need to get all high and mighty about it.