This is a basic pulley, and pretty much what you would expect. As a teaching tool, it shows the function of a pulley clearly, and a pair of them can be rigged together to show mechanical advantage in a very easy to understand way. They are lightweight, but built well. We used a 1 kg weight with ours with no apparent strain. They should be last for many years. If you need them, the price is definitely right and HST is a great company to do business with!
These are light duty pulleys, but they work just fine as a teaching aid for simple machines. If you are rigging two pulleys together to show mechanical advantage, HST is correct. You definitely do need some weight on the lower pulley(s) in order maintain tension on the string while you continue stringing the pulleys. However, once the setup is done, they work just fine and are a great value.
Exactly what I needed for a fraction of the price than I had found elsewhere. I am a bargain shopper with 2 homeschool children and this is becoming my one stop shop for all my science needs! I would buy other products made by the same company based on my experience with this item. No problems at all!