2010 JUL 3: Tampa Bay's Dan Wheeler (35) pitches during a Major League Baseball game between the host Minnesota Twins and Tampa Bay Rays at Target Field in Minneapolis, MN. Tampa won 8-6.

The Sox continued wheeling and dealing this week, adding relievers Bobby Jenks and Dan Wheeler to the pen — along with a slew of minor league arms.

Jenks and Wheeler will be welcome additions to the back end of the bullpen. Though Jenks may be coming off a rough season by conventional standards — dropping in a 4.44 ERA despite nailing his key peripherals.

Those peripherals earned Jenks his two-year $12 million deal — and for good reason. With a 10.42 K/9 rate and 3.09 BB/9 rate, the White Sox closer was able to compile a 2.59 FIP to go alongside a 1.5 WAR.

Also of note was the sustained velocity on Jenks’ fastball, which averaged a cool 95.0 mph. Many have speculated that the decline in Jenks’ strikeout rate was the result of a loss in fastball velocity, which fell from 97.0 in 2005 to 93.8 in 2008. This likely played a role, though mechanics and fatigue may have also played a role.

But it isn’t all rosy with Jenks as the Sox’ new setup man. Despite the strong peripherals, there are parts of his performance that don’t add up to stardom. While his control and groundball indicators are still excellent, his strikeout numbers give reason for pause.

In particular, Jenks’ 81.3 percent contact rate needs to improve in order to sustain such a lofty strikeout total. Most notably, his 89.7 percent zone contact rate won’t result in another strikeout rate north of 9 per 9 anytime soon.

Nevertheless, Jenks is a very good reliever who should have no problem registering an ERA in the mid-3.00s, which will be more than acceptable for an AL East team with championship aspirations.

Dan Wheeler was the other primo signing by the Sox this past week, inked for $3 million on Saturday. The former Rays bullpen hand is coming off another stellar season — his third consecutive with an ERA under 3.35.

The Wheeler signing is certainly an interesting one, however, as his superb ERAs are largely the product of extremely low BABIPs. In fact, his lowest of the last three seasons occurred this year, with a .243. The other two were .202 and .203 in 2008 and 2009, respectively.

What makes Wheeler so interesting is the fact that he has been able to sustain his low BABIPs. Though examples of pitchers with this degree of control over their BABIP are rare, there are instances of hurlers with some control over BABIP.

Therefore, this signing could be a well calculated move by the Red Sox, as they may have found an inefficiency in the free agent market — signing pitchers who do not fit the sabermetric stereotype of a successful pitcher. It’s difficult to say whether or not Wheeler will be able to repeat his success, but for $3 million it may be worth the risk — especially since Wheeler is a worthy reliever with or without the BABIP boost.

Aside from BABIP, however, Wheeler does have a checklist of to-do items to fix before 2011 kicks off. In particular, he will have to adjust his approach on the mound and throw more strikes.

Wheeler has always been a command specialist, throwing nearly 55 percent of his pitchers inside the zone in his career. That changed in 2010, however, as that rate dropped to just 45.5 percent.

While drops in zone percentage are not always troubling on their own, the fact that Wheeler did not see an accompanying increase in O-Swing percentage is cause for concern. Oftentimes, pitchers will respond to hitters swinging outside of the zone by throwing more chase pitches. This does not seem to be the case with Wheeler, however, as his O-Swing was largely unchanged from 2009.

Though Wheeler remains a very talented pitcher, these rates bear watching.

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