My Ice boots have a thick semi-hard rubber sole. I found that using a standard hex drive sheet metal screw (#8 X 1/2 inch long), can be driven into the sole without penetrating through it. The rubber holds the screw in well and the sharp hex head bites the ice well. When one wears out just replace it. I bought a box of 100 screws for $4.40. I installed about 34 screws per boot and they work great and were easy to put in. The thickness of the sole determines the length of the screw, I went about 2/3 rds the thickness to determine the length of the screw