What makes a White Sox reliever an extension candidate?

The three-year, $8 million extension that Nate Jones signed last week didn't spark an immediate reaction out of me, which is by no means a negative. If the first thought isn't "Why did they do that?" the evaluation is already off to a decent start.

White Sox relievers are just different animals, is all. We could see Chris Sale's extension coming, and we popped champagne when he signed one. When Sale signed one, we anticipated Jose Quintana doing the same, and Rick Hahn went 2-for-2 with those easy calls.

When it comes to the bullpen, the Sox don't strike these deals nearly as often.

Granted, it's mostly due to a lack of candidates. The Sox haven't churned out a whole lot of high-leverage types from within, but they've covered for that deficiency by acquiring setup guys with staying power. At least until Jesse Crain gave out, anyway.

Moreover, their best promoted arms found immediate success in the closing role. Bobby Jenks and Addison Reed started racking up saves as rookies, which put them on the path to big arb-year paydays even if they weren't the greatest at their jobs. That makes an early extension difficult to negotiate -- either the player risks giving up a lot of money, or the team is leaving itself vulnerable to overcommitting to an early plateau. Jenks and Reed both showed signs cautioning the latter; Jenks required a lot of maintenance both physically and mentally, and the fastball-first Reed lost velocity.

These conditions forming the collective case, the White Sox locked up just three relievers since 2006 before Jones signed his contract. And as a hard-thrower with question marks, Jones fits right in.

The White Sox struck gold when they signed Matt Thornton to a three-year, $3.25 million extension with two club options back in April of 2007. We don't need to go into how he paid for himself multiple times over.

That helped nullify the deal from a few months earlier, when the Sox gave a three-year, $6.45 million contract to Mike MacDougal. The Sox thought he'd proved his worth by pitching well over 25 games in his first half-season in Chicago, but he collapsed in his first full go-around, and he ended up getting cut loose halfway through his contract.

Thornton and MacDougal established both ends of the spectrum, yet Sergio Santos doesn't fall in between either. He signed a three-year, $8.25 million extension at the end of the 2011 season, one in which Santos saved 30 games with nasty strikeout numbers.

Somehow, the Sox didn't pay any of that extension, as they traded him to the Blue Jays in December. They didn't miss out on anything, as all sorts of injuries have limited Santos to just 68 ineffective MLB innings over the last four seasons.

Aaaaaaand ... that's it. One of those contracts hit the jackpot, another one busted, and another one turned into a billion Nestor Molina selfies. Good luck drawing a conclusion from that array of outcomes, which is why I didn't have an immediate reaction for the Jones news besides "can't hurt that much."

What we can do is see a couple shared traits despite the disparate results. Ironically, one of them is a lack of ironclad sustainability, at least by reliever standards. Thornton had Tommy John surgery in 2002 and couldn't iron out his post-operation stuff with his original organization. MacDougal had a difficult time staying healthy in Kansas City, and Santos was a shortstop who was born again as a reliever. Jones fits in as a guy who made his debut at the rather advanced age of 25, then lost a year and a half to two surgeries.

The other: Uncanny stuff. MacDougal and Santos both spun wipeout sliders, and Thornton torched radar guns. They may not have parlayed their gifts into years of high-leverage success, but one could see how they might, and one can see how Jones fits in here.

That's what the Sox are betting on, anyway. The good news is that Jones is closer to Thornton than the other two -- when he's been healthy, he's been a reliable seventh-inning guy, with flashes of better. Regression tends to set in before anybody can dream too big, like last September, when he gave up three homers over four appearances just as the beat guys started publicly pondering a replacement for David Robertson.

I'd expect Jones to keep bonking his head against that ceiling, just based on track record and those unique bow-and-arrow mechanics. That's not so much a scouting statement as an identifier. He's a pitcher with an unusual style and a suddenly iffy health report, so the Sox should be content if he's available the whole season and making Zach Putnam the fourth-most important righty, because the bullpen is shakier when Putnam the non-Jake Petricka fallback for eighth-inning opportunities.

That expectation strikes a good balance between eminently reasonable and incredibly helpful, so anything beyond that would be gravy. Then again, Jones throws so damn hard that he might just clear that last hurdle, and the Sox are now beautifully set for that outcome.