Originally Posted by TexasTitleistGuy
690.MB is Titleist's largest most forgiving blade. They have the most offset, and the largest sweet spot among all the Titleist irons. Very thin topline and traditional appearance. The muscle position in the irons is very low yielding a low center of gravity and a higher ball flight.
The 680's look similar to the 690's appearance wise, but are a much smaller blade with less offset. Consider these Titliest's player's irons and are found in Ernie and Adam Scott's bags. The muscle is positioned much higher and lowers ball flight more than the 690's.
The 670 is a whole different animal. It is the smallest blade Titleist makes and is heel weighted creating the lowest ball flight of any club in the titleist line. They have a thicker topline at address. The biggest difference though is in the sole, the 670's have a wider sole with more bounce combined with a blunt leading edge for players who like to take a pretty substantial divot. These aren't sweeper's clubs. I don't know if he still does, but I'm positive DLIII had these in the bag last year.
The T stamps are replicas of Tiger Woods irons when he started out with Titleist. They are the hallowed Titleist 681's (which are some argue are the best irons Titleist ever released) 1° strong with golf pride tour velvet cord grips and a T stamped where the 681 would go. When Tiger signed with Nike, the 681s were replaced by the 680's and are pretty similar construction wise. There are supposedly only 50 sets in existance.
Hope that helps