Gentlemen I put to you the best handtool invention, is the screwdriver. The hammer is good for only putting nails in an making permient fixtures. Where as the screwdrive allows one to put together and take apart without wrecking everything in an easy fashion. Thnk on it for one minute, all of the things that we screw together, many things in construction, mechanics. One does not have to posess great strenght to use it effectivily , the addition of the modern electric and cordless drills increase the uses of screws, with even less effort. As for screw heads the most popular in the past was the flat head, then we have the PhilpsHead or star head and then the best of all a Robertson head, or square head invented by a canadian.