MB-3 – 2.5″ wheel double: Used with models 1703-A and 1403-A Center Take-Off Live End Pulleys. MULE BLOCKS are a means of allowing line to pass over or around obstacles without rubbing or binding. When a curtain needs to be manually operated from a remote location, or a machine’s location does not provide proper cable alignment, mule blocks can solve your rigging issues. Cord and cable will be protected from undue wear and operation will not be hindered by obstacles (HVAC units or ductwork, structural members, lighting fixtures etc.) or excessive drag. Overall dimensions: 5″ L x 4″ W x 3-1/2″ H. Weight: 2 lbs. 8 oz.