This means that when the angle of the line on the block is at 60 degrees, the maximum load on the block has been reached so the line load can be at most the full Safe Working Load. For example, if the block has a SWL of 900kg, if the line through the block is to be at 60 degrees, then the line load can be at most 900kg. Similarly if the angle of the sheet on the block is 180 degrees, then the max load on the line would be half the SWL. In the case of our 900kg SWL block, the max load on the line would be 450kg.
Once you know the max load that you need your block to manage, please use the table below to help identify the range of block to investigate. Please note there are high load blocks available in the single block range to increase the SWL. These high load blocks are for the 40-70 series single blocks.