Rigging blocks and pulleys help you change the direction or strength of a pull on a rope. CMI blocks are the most regular and least expensive version. These metal blocks require you to use a screw to open them up. Meanwhile, ISC spring blocks are a bit pricier than CMI blocks.
But they’re easier to use because they open with a spring instead of a screw. They also come in different sizes.
Small blocks are ideal for use with tiny ropes. One famous kind of small block is the ISC RP 48. Meanwhile, DMM impact blocks are the top-of-the-line rigging blocks, the most expensive and the fanciest. These aluminum blocks use a screw mechanism to open (like CMI blocks). They also have a special loop that you can clip onto your harness.
ISC spring blocks are the best value for your money, but DMM impact blocks are the strongest. Typically, arborists set up these pulleys and blocks strategically in the tree. Doing so creates a tree-friendly pulley system. Then, they attach ropes to the branches they want to cut or remove. Instead of chopping away and letting the branches crash to the ground (which could be dangerous and damaging), they use the pulleys to lower them down gently.
It’s a giant game of tug-of-war, but instead of pulling, they’re lowering these heavy branches with finesse. The pulleys help distribute the weight and control the descent. Because of this, it’s not a chaotic freefall. It’s all about precision and safety.
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