I am a huge fan of all types of grip training equipment - I have and regularly use Ironmind hand grippers, David Horne's Vulcan gripper, the FBBC vertical bar and Bomb as well as a variety of block weights, thick handles, bending gear, etc. And while it would be tough to get me to part with any of those implements, one of my very favorite pieces of grip training "equipment" has been in my gym bag since long before I ever invested any time in training my hands directly. I've long been a fan of taking my favorite exercises, movements that I know really work, and adding a new element to them to see if I can push the envelope when it comes to achieving results - sometimes this tactic hits, other times I realize that the original movement has become a mainstay in my routines because it doesn't need much (if any) altering.
One of the most successful "add ons" I've made to my workouts to improve grip strength has been the simple addition of a gym towel (this should probably go without saying, but make sure it is a strong towel capable of holding your body weight without shredding) to certain lifts. This might sound a bit unusual, even ridiculous to some of you, but bear with me here...
The first movement I tried it with was pull ups (this certainly wasn't my innovation, I've seen many others throw a towel over a pull up bar before). I knew it would be more difficult than a conventional pull up, just didn't expect it to be that difficult. I had been training grip for a few years, primarily with grippers, but the instability/inconsistency made the pull ups far more taxing for me than traditional pull ups or what I considered to be more traditional grip training (grippers, thick bar, etc).
While adding towel pull ups as a finisher on back/arm day probably would have been enough to give a nice boost to my grip, I instinctively wanted more. What else could I throw a towel over to create a killer grip circuit?