Without any contact, the majority of the position drills do very little to improve or reduce current draft projections. The NFL uses the combine to corroborate or trigger further evaluation for players. In my opinion, the most important part of the process (for the OL) is the interview, medical, and physical measurements. I've compiled the list of arm length measurements from the 2013 draft to help guide your evaluation of OL in this year's combine.
These are compiled arm length results for OT taken in the 2013 draft. You can see in this limited sample that the Offensive Tackle drafted in round 1-3 have a 34"+ arm length, on average.
|2nd & 3rd Round||OT||34||34||34|
|4th & 5th Round||OT||33.77||33.375||34|
|6th & 7th Round||OT||33.5||32.625||34.375|
The Offensive Guards have shorter arm lengths than the Tackles, but arm lengths are still very important. When the talent decreases below the 3rd round, NFL teams default to guards with longer arms.
|2nd & 3rd Round||OG||33.4||32.75||34.125|
|4th & 5th Round||OG||34.33||34||34.875|
|6th & 7th Round||OG||34||32.25||35.5|
The Center position clearly has less to do with arm length than it has to do with athleticism.
|2nd & 3rd Round||C||N/A||N/A||N/A|
|4th & 5th Round||C||33.5||32||35|
|6th & 7th Round||C||33.5||33.5||33.5|