 Industrial jacks can be rated for many tons of load.The personal name "Jack", which came into English usage around the thirteenth century as a nickname form of "John", came in the sixteenth century to be used as a colloquial word for 'a man (of low status)' (much as in the modern usage 'jack of all trades, master of none').From here, the word was 'applied to things which in some way take the place of a lad or man, or save human labour'.