First of all thanks for all of your replies they are about what I have discovered/done/put into practice etc.
In the case of advising them, my target market speaks about 15 different languages I am fluent in 2 and can order a beer in 5. Telling the rest how to be delicate well.... 
BUT I have discovered that even if you demonstrate explain and even say that there is no guarantee if they cross thread they try to enforce a guarantee. The worst being the brits!! Now they want an instruction manual on how to operate a pen What on earth do they teach them at school?? Sorry since its the 40 year old parents what on earth did they teach them at school?
When you see Charles Atlas approach and pick up a junior gent and try to use it as a chest expander then say well actually its a screw thread and then he turns it clockwise because he is a (rude bottom) what on earth do you do?
my prize will go to someone who invents a decent tungsten carbide thread mating into a carbon fibre reinforced by graphene thread for £1.20 per pen kit!!
In the meantime more 7mm biros because they sell well at the schools' return (la rentrée). Sigh!
Have fun all.
PG
