As a user of crutches 15 years now, it's been a lifetime of lessons on crutches. From balancing act to the point of being a self driven individual (like literally) it's impressive. When one buys a crutch, the new tips ie the rubber part that touches the ground, are usually rounded with round threads and have suction. This tips are best suited for slippery floors since with the suction effect it can easily grip the floor reducing the chances of falling. But problem is, we use the crutches on all terrains hence the tips wear out,hardening and the suction disappears. That's why we'd go to a shoe maker to make new tips from worn out rubber tires. The treads on this are suited for all terrains. But for someone who uses crutches only indoors, the rounded tips with round treads and suction are best suited.