A friend of mine bought a bicycle inner tube, wiped the white stuff of and cut himself a slip on grip. I thought it was an after market product until he told me what he had done. He did a great job and it felt great.
I've used the Bicycle tube grip on my keltec, but the Hougue slip grip in small works very well on the Pt111 and also it helps in pointing the gun. It allows you to use more pressure with your middle finger and the gun actually shoots straighter. For me at least.
Houge Handall Jr., works great but hard as heck to get on, I used a little dish soap and spit to get it to slide on but absolutely love the way it fits my PT111 Mil Pro. I also trimmed the bottom edge when I had it in final position to align with bottom of gun.