There are a few things to consider when choosing a rope pulley. The first is the size of the sheave, which is the wheel that the rope runs over. The larger the sheave, the more contact there is between the rope and the pulley, which can help to reduce wear and tear on both the rope and the pulley. The second thing to consider is the material that the pulley is made from. Some materials, such as nylon, can be very slippery, which can cause problems if your application requires a lot of friction. Other materials, such as stainless steel, can be very durable but may not offer as much friction. Finally, you'll need to decide what type of attachment point you need for your application. Some pulleys come with built-in hooks or eyes, while others require that you purchase separate hardware to attach them to your structure.