You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
         [0001]    1. The Field of the Invention  
           [0002]    The present invention pertains to beam pumping wells and, more particularly, to beam pumping wells having pull tubes which attach to the plunger portion of a reciprocating downhole pump.  
           [0003]    2. The Prior Art  
           [0004]    The typical pull tube adapter used on reciprocating beam pumping wells includes box X threads and is made for connecting a pull tube to the plunger portion of a reciprocating downhole pump. There are two types of standard reciprocating downhole pumps which can use such pull tube adapters. The first is a hollow tube pump and the second is a traveling barrel pump.  
           [0005]    The disclosed lower pull tube adapter is an improvement over prior art adapters in that it provides the ability to use a larger pull tube for any given pump size. The use of a larger pull tube is desirable for several reasons. First, strength is added to the pump since larger, heavier parts have greater durability and break less frequently. Secondly, larger pull tubes have less flexing thereby lowering the chance of both metal fatigue and wear of the pull tube. The larger pull tube adapter allows for additional fluid flow.  
           [0006]    The present lower pull tube adapter may be used with a downstroke pump, that is a pump in which fluid is pumped out of the well only on the downstroke of the pump and no fluid is pumped on the upstroke of the pump. A description of such a pump can be found in my U.S. Pat. No. 6,368,084, the disclosure of which is incorporated herein by reference.  
         SUMMARY OF THE INVENTION  
         [0007]    The present lower pull tube adapter has an enlarged body portion and an enlarged seal surface so that one size pull tube adapter may be used for a wide range of reciprocating downhole well pumps of different sizes and types. When used on a downstroke pump, the present lower pull tube adapter enables using one size pull tube and one size pull tube guide may a wide range of pump sizes. When used with a standard hollow tube pump or traveling barrel pump, the present lower pull tube adapter allows for greater strength and rigidity with more fluid flow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The present invention will now be described, by way of example, with reference to the accompanying drawings in which:  
         [0009]    [0009]FIG. 1 is a longitudinal section through the subject invention;  
         [0010]    [0010]FIG. 2 is a perspective view of the subject invention; and  
         [0011]    [0011]FIG. 3 is a side elevation showing the subject invention exploded from a pull tube and collar. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    As shown in FIG. 3, the pull tube  10  has a hollow cylindrical body  12  which is externally threaded on an upper or first end  14  and internally threaded on a lower or second end  16 . A cylindrical collar or guide  18 , having an inwardly directed annular flange  20  on one end, is fitted over the lower end of the body  12 .  
         [0013]    The subject pull tube adapter  22  has a generally cylindrical body  24  with an externally threaded pin or first end  26  of a first diameter and an internally threaded second end  28  of a second larger diameter with an outwardly directed shoulder  30  between said ends. An axial bore  32  extends through the adapter and at least one radial bore  34  extends from the axial bore  32  to the surface of the adapter adjacent the shoulder  30  on the larger diameter portion of the adapter.  
         [0014]    The first end  26  of the subject adapter engages the internally threaded lower or second end  16  of the pull tube  10 . The shoulder  30  engages the flanged end  20  of the collar  18  to form a sealing interface between the subject adapter  22  and the pull tube  10 . This threaded engagement of the internal threads  16  in the pull tube  10  with the external threads  26  of the pull tube adapter  22  provides a larger sealing surface and gives the user the option of using the collar or guide  18  to keep the pull tube  10  centered within the pump. Keeping the pull tube centered within the pump prevents wear of the adapter from metal-to-metal frictional contact.  
         [0015]    The subject lower pull tube adapter also allows for the use of one size of a pull tube guide instead of the multiple sizes of pull tubes presently in use. As shown in the attached figures, a collar is held in place by the threadable attachment between the pull tube and the lower pull tube adapter. Typically, a pull tube for a 1¼ inch bore pump would be {fraction (15/16)} inch in diameter. The lower pull tube adapter of the present invention will allow the use of a pull tube which is 1⅛ inches in diameter. This allows for greater strength and rigidity, and a larger seal surface with greater fluid flow.  
         [0016]    The present invention may be subject to many modifications and changes without departing from the spirit of essential characteristics thereof. The present specification should therefor be considered in all respects as illustrative and not restrictive of the scope of the invention as defined by the appended claims.

Summary:
A lower pull tube adapter has an enlarged body portion and an enlarged seal surface so that one size pull tube adapter may be used for a wide range of reciprocating downhole well pumps of different sizes and types.