DIY Grip Balls...or...Softball pullups

I don't know what to call them.  They're softballs that you do pull-ups with in order to build your grip.  Here's the short of it. 

Parts List:
2-Softballs
2-Eye Screws (recommended 7/16")
2-Lashing Straps (you can use rope if you don't care about changing height, or chains if you have q-links or carabineers)

Simply put:
Screw the eye screws into the softballs and hang them from a bar, rafter, tree branch, etc. with the lashing straps.  So easy, cheap and effective!

Here's a video of me putting a pair together for less than $10...

Homemade Softball Grips