Selection Guide

Some of the blocks shown in Crosby Group literature are named for their intended use and selection is
routine. A few examples include the “Double Rig Trawl Block” used in the fishing industry, the “Well Loggers Block” used in the oil drilling industry, and the “Cargo Hoisting Block” used in the freighter boat industry.
Others are more generally classified and have a variety of uses. They include snatch blocks, regular wood blocks, standard steel blocks, etc. For example, snatch blocks allow the line to be attached by opening up the block instead of threading the line through the block.
This feature eliminates the use of rope guards and allows various line entrance and exit angles to change direction of the load. These angles determine the load on the block and/or the block fitting. (See “Loads on Blocks.”) Snatch blocks are intended for infrequent and intermittent use with low line speeds.
A tackle block is one element of a system used to lift or drag a load. There are other elements in the
system including the prime mover (hoist, winch, hand), supporting structure, power available, etc. All of
these elements can influence the type of tackle block required. When selecting a block for the system in your specific application, you should consider the other elements as well as the features of the blocks shown in Crosby Group literature.
To select a tackle block to fit your requirements, consider the following points:

1. Are there regulations which could affect your choice of blocks, such as federal or state OSHA, elevator safety, mine safety, maritime, insurance, etc.?
2. What is the weight of the load, including any dynamics of impacts that add to load value? You must know this to determine the minimum required Working Load Limit value of the block.
3. How many parts of line are required? This can be determined given the load to be lifted and the line pull you have available. As an alternative, you could calculate the line pull required with a given number of parts of line and a given load weight. (See “How to Figure Line Parts.”)
4. What is the size of line to be used? Multiply the available line pull by the desired safety factor for wire rope to determine the minimum catalog wire rope breaking strength; consult a wire rope catalog for the corresponding grade and diameter of wire rope to match. You should also consider fatigue factors that affect wire rope life. (See “Sheave Size & Wire Rope Strength.”
5. What is the speed of the line? This will help you determine the type of sheave bearing necessary. There are several choices of bearings suitable for different applications including:
   Common (Plain) Bore for very low line speeds and very infrequent use (high bearing friction).
   Self Lubricating Bronze Bushings for slow line speeds and infrequent use (moderate bearing friction).
   Bronze Bushing with pressure lubrication for slow line speeds and more frequent use at greater loads (moderate bearing friction).
   Anti-friction Bearings for faster line speeds and more frequent use at greater loads (minimum
   bearing friction).
6. What type of fitting is required for your application? The selection may depend on whether the block will be traveling or stationary. Your choices include single or multiple hooks with or without throat latches and shackles, which are the most secured load attachment. You should also decide whether the fitting should be fixed, swivel or swivel with lock. If it is a swivel fitting, then a selection of thrust bearing may be necessary. There are plain fittings with no bearings for positioning at no load, bronze bushed fittings for infrequent and moderate load swiveling, and anti-friction bearing equipped fittings for frequent load swiveling.
7. How will the block be reeved and does it require a dead end becket? (See “The Reeving of Tackle Blocks.”)
8. If the block is to be a traveling block, what weight is required to overhaul the line? (See “How to Determine Overhaul Weights.”)
9. What is the fleet angle of the wire line? Line entrance and exit angles should be no more than 1 1/2°.
10. How will the block be maintained? Do conditions in your application require special maintenance
    considerations? (See “Tackle Block Maintenance,” and “Fitting Maintenance.”)