2015 Steelers depth chart: Inside linebacker deepest position on the team

The Pittsburgh Steelers hit free agency hard last year, bringing in a handful of veteran players to earn starting roles and improve depth.

Here is a position-by-position look at the Steelers depth chart going into this year's March 10 start of free agency.

PITTSBURGH -- Unlike their partners at outside linebacker, the Steelers appear to be set on the inside with six players under contract.

Lawrence Timmons should lead the way again this year. The club's best all-around player on defense, Timmons will be the Steelers second-highest cap hit at $12.57 million as well and has two years remaining on his mega-contract. This will be Timmons' ninth NFL season, but he is just 28 years old (29 in May) and already has been a mentor to the young Steelers backers. With 141 tackles, two sacks, six quarterback pressures and two pass breakups, Timmons numbers finally added up to a Pro Bowl selection after several snubs.

Sean Spence, Vince Williams and Ryan Shazier make up the trio who played next to Timmons, and they credit him for their success. Shazier, last year's first-round pick, was hampered by injuries most of the season. But expect him to get the bulk of the playing time if he can stay healthy. He is under contract for three more years with a fourth at the Steelers option. Expect him to play an even bigger role this season, as long as he can stay on the field. Knee and ankle problems hampered him, but he should be ready to go this year.

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Spence's performance was miraculous last year, but not because he doesn't have the talent. Spence suffered a gruesome knee injury during his rookie preseason in 2012 and missed two years. So, 2015 is the final year of his rookie contract, but if his production continues -- 54 tackles, one sack, four quarterback pressures, a pass breakup and fumble recovery -- he will be extended with no hesitation.

Williams basically shared time with Spence, while Shazier was on the shelf, and he has played a lot of football in two NFL seasons. A rigorous offseason conditioning program gave Williams a chance, and his improved play led to more opportunities. He has two years left on his rookie deal. Williams was at inside linebacker next to Timmons when the Steelers were in the nickel, and Spence was there in the base 3-4.

Terence Garvin played exclusively on special teams, but he emerged as the Steelers top kick and punt coverage specialists. He is extremely valuable in that role and makes a minimum salary. He was an undrafted, spring tryout invitee and made the team. He tied for the top spot with 15 special teams tackles.

Roosevelt Nix is the other inside linebacker on the Steelers roster. He was a 5-foot-10, 237-pound pass-rusher at Kent State and tallied 20 tackles behind the line, 10 sacks and four forced fumbles. He must learn a new position, but he will be 23 March 30 and has the time to learn on the job. He is an excellent practice squad prospect.