and the prongs 2 will be elastically deformed providing the required clamping action fig4 shows a sample design in which the bolt 11 of fig3 is replaced by a ball 13 the ball 13 is pressed into the two recesses 14 in the extensions 9 the effect of this is the same as that of the bolt 11 and at a given value of elasticity for the other parts the diameter of the ball 13 determines the amount of clamping force fig5 shows a third sample design in which the same result is achieved by using a rivet 15 to bring the two prongs 2 closer together to provide the necessary compressive force a nut and bolt could also be used instead of a rivet fig6 illustrates a sample design in which only the lower prong 2 has a groove 3 this design can be employed when the wire 4 or the end of the wire is thick enough that two transversal grooves 16 can be made in it the lower sapphire 5 establishes contact along two generatrices with both the groove 3 in the lower prong 2 and the lower groove 16 in the end of the wire the upper sapphire 5 establishes contact along two generatrices with the upper groove 16 and along.