By 'flat end', I assume that you mean 'crimped end', where the end of the tube is flattened, and in some cases bent through a right angle.  These are normally only used for fixing precast and the size is usually only up to M30.  They are not generally available as an Rd lifting thread, and cannot therefore be used with Rd threaded lifting heads.  Tubular lifting sockets on the other hand are normally made with an Rd thread as part of a system.   More specialised types have a plate or a waved reinforcement bar on the lower end to spread loads.  They are fully compatible with Rd threaded lifting heads.  (The difference between Metric threads and Rd threads is explained in the Lifting and Handling section of Key2concrete).  In addition, Rd sockets go up to a maximum size of Rd52.

The important things to bear in mind when choosing lifting sockets are:

• Always use a reputable supplier who can back claims up with full testing certification.  Most construction sites will not allow lifting tackle to be used that does not have the correct paperwork.
• Only use lifting heads that are designed for lifting concrete.  Some similar lifting heads are available that are designed for lifting items such as steel blocks.  Whilst these will fit into an Rd socket, they are rated differently and can cause overstressing, particularly if turning concrete.
• Always incorporate the reinforcement around the socket as shown in the supplier's literature.  With simple sockets a bar is usually passed through a hole in the end of the socket.
  

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