Inserts for the crossing points of tennis racket stringing
FIELD OF THE INVENTION 
     The invention relates to inserts for strung tennis rackets, which are to be located at the crossing points of the strings, particularly natural strings, the inserts being formed by a lubricated absorbent material, i.e. felt, leather or similar material of natural or synthetic fibers. 
     BACKGROUND OF THE INVENTION 
     From the Austrian Pat. No. 82519 it is known that spacers or inserts may be in the form of leather pieces, which are located between two strings at their crossing point. These leather pieces, however, cannot sufficiently protect the strings against wear, which is caused by mutual friction. 
     SUMMARY OF THE INVENTION 
     The invention solves this problem by using an insert, which is impregnated with a liquid lubricant, for example a silicone base oil. Such a lubricant is capable of eliminating the mutual friction at the crossing points of the strings to a large extent, resulting in a considerably longer lifetime of the stringing. It is therefore not required that the inserts prevent the strings from touching; their main function is is to lubricate the contact points between the strings. In one particular embodiment of the invention, the insert is retained in a known crosspiece, preferably of plastic material. Such crosspieces are known in various shapes and have been described in the Austrian Pat. No. 357 072 and the German Pat. No. 2 258 872. 
     A preferred embodiment of the invention is charcterized by the insert being retained in a crosspiece of known shape in the form of a ring with the axis perpendicular to the plane of the strings, to be inserted between the crossing point of two strings. This ring is preferably formed with diametrically opposed indentations at both ends which are offset from one another and approximately semicircular in cross section and are to engage and retain the two transverse strings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawing, in which: 
     FIG. 1 is a plan view of an insert according to one embodiment of the invention; 
     FIG. 2 is an axial sectional view taken along line A--A of FIG. 1; and 
     FIG. 3 is an overall view of a tennis racket with inserts according to the invention. 
    
    
     SPECIFIC DESCRIPTION 
     The insert 1 has a crosspiece in form of a ring, which has on each end face 2 two approximately semicircular indentations or recesses 3 for the strings 4 of a tennis racket R and retains, as an insert a pad 5 of absorbent material as previously described. The crosspiece is appropriately made of a flexible plastic. As a suitable lubricant to be taken up by the pad 5, a siliconebase oil can be used. 
     Such a lubricant may also contain an impregnating substance for the material of the strings to further extend their durability. The scope of the invention is not restricted to the form described in the drawings; it is possible, for example, to omit the semicircular indentations 3 in the cross piece, if the plastic material of the ring is sufficiently flexible by itself to be deformed when being inserted between the strings and is thus held in place. Using a suitable material, the insert, impregnated with the lubricant, may be sufficient by itself to be placed between the crossing point of strings without the crosspiece. 
     It is not necessary to insert spacers at all crossing points of the strings; in many cases it is sufficient to use the spacers surrounding the area of the sweet spot of the racket as illustrated in FIG. 3.