Well, if I go to my local steel supplier and ask for a length of half-inch pipe, he will get out a length of half-inch ID (nominal) pipe, such as water pipe etc.
If I ask him for a length of half-inch tube, he will get out a piece of similar looking stuff that is half-inch OD and the ID is left un-noted, and depends on the wall thickness.
The "pipes carry liquids; tubes are structural" line does not hold true when you think of stainless bundy tube used for brake lines and fuel lines on vehicles. The bundy tube carries liquids, yet is measured by the OD and hence is tube not pipe.
But I am afraid the screws vs bolts argument, Neil, is a lost cause. It seems if I go into any local fastener specialist shop and ask for 3/8 UNF by 3 inch hex-head machine set screws, the counterman will invariably come back with bolts; that is the thread does not extend all the way up the shank to the head.
Edited By Hopper on 05/03/2016 11:11:22