What is this "thing" on Billy Butler's bat? What is it for?

[camarokids]

I have never seen one of these things before.What is it used for?

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[Juan Gris]

It looks like some sort of time travel device but I don't believe Billy Butler was on the 1985 World Series squad... he must be from the future.

Sorry, couldn't resist. My guess is it's a batting weight.

[jetersbatboy]

My son's team use it, it's a bat weight.

http://varobaseball.com

[metsbats]

It's a TATC bat weight:)

[camarokids]

Thanks for the answers, all of them :).... Looks pretty cool....

[TNTtoys]

It's a TATC bat weight:)

Dang! Another TATC item I am missing for my collection.