Improving the offensive line has been an apparent theme for the Indianapolis Colts off-season. In the first and second rounds of the 2011 NFL Draft the Colts selected Anthony Castonzo and Benjamin Ijalana, respectively, in order to address the need at offensive tackle. Charlie Johnson is a spectacularly dynamic offensive lineman who is capable of playing four positions on the line, but would be much better inside or at right tackle. Veteran right tackle Ryan Diem's production has noticeably declined over the last two seasons and he is commanding a $5.4 million contract in 2011. This leaves players like Ijalana, Johnson, and second-year player Jeff Linkenbach as front-runners for right tackle. If Ijalana or Johnson move to right tackle, the guard spots will still be filled by a combination of Mike Pollak, Kyle DeVan, or first year starters Jacques McClendon and/or Jaimie Thomas. Linkenbach showed in 2010 that he is not ready to play inside in the NFL. McClendon and Thomas would be unknowns. Pollak has been inconsistent and has lost his starting job numerous times over the last two seasons. It is for this reason that Chris Polian and the Indy front office could be interested in signing a veteran guard in place of letting Diem's high contract go. In fact, if Indianapolis signed one of the following three veteran guards the offensive line could be one of the strongest units on the team when January rolls around -- assuming the rookies develop as projected. Logan Mankins - previous contract 5 years, $6.4 million Harvey Dahl - previous contract 1 year, $2.5 million Justin Blalock - previous contract 4 years, $5 million Mankins is a 29-year old veteran who is unhappy in New England and should be very familiar to the Colts. Adding a player of his caliber would certainly bolster the offensive line and give players like Jacques McClendon an opportunity to focus on taking over for veteran center Jeff Saturday in the future. It will likely cost the team $3.5-4.5 million a year cap hit to sign a player looking for a new contract with his resume -- which may price him out of the Colts market. Dahl is the kind of big bodied player who can play inside or out and should be an immediate improvement in the ground game. He is 30-years old and has the experience to attract the attention of suitors but could come cheaper than Mankins. A $3-4 million a year cap hit could help the Colts offensive line reach an elite level. Blalock is potentially the most attractive player on the market for a team like Indianapolis because he is 27 years old and has improved in each of his first four years. He sticks with blockers well and has not reached a dominant level but is superior to what the Colts have currently and could be nabbed for a 3-4 year $3-4 million cap hit. Like the other free agent options he would be an immediate improvement for the ground game and would allow lesser experienced linemen to play a backup role and continue developing. With two offensive linemen already added in the off-season, there is a good likelihood the Colts will stay out of the free agent market. That said, if Indianapolis chooses to part ways with Diem, it is not unreasonable to find another offensive linemen to replace him. If Ijalana, Johnson, and Castonzo are who the team has pegged as the starting tackle options, a guard would make the most sense.