What is the difference between tour clubs and regular golf clubs, i.e. Callaway x-20 and x-20 tour?

Well the two clubs you mentioned are both retail clubs. The X-20 Tour is designed for a better player because it has less offset and sits squarer. The tour name is just the model, nothing to do with tour. The clubs tour players use are usually clubs you can't find on the retail market, or won't see them for a long time. Most testing for clubs that eventually end up in retail is done on the various tours. However, there are some clubs that you see on tour that are the same as retail. The only difference is the custom work that goes into them as well the serial numbers on the hosel. Tour irons will have either no serial number or Txxxx number. A golfer on tour can use any clubs he wants, though most will use tour equipment given to them by the companies. There are many stories of golfers breaking a club and going to a retail store to buy a replacement for a tournament. more