fig1 and 14 the total width of the coupling mechanism can also be reduced by pivoting the width adjusting spacer member 2 backwardly to a predetermined position during assembly a front opening of the wiper arm 3 is slid along one end of the connector 1 in a favorable direction for assembly thereto where this movement will depress the engaging member 14 of the connector 1 when the wiper arm 3 has slid to a predetermined position the engaging hole 31 of the wiper arm 3 will be in alignment with the engaging member 14 where the pressure exerted on the depressed engaging member 14 will be released for the engaging member 14 to return to the original position hence the engaging member 14 will clip in into the engaging hole 31 for the connector 1 to assemble to the wiper arm 3 and where the width adjusting spacer members 2 can be received in the wiper arm 3 referring to fig8 according to another embodiment of the instant disclosure the amount of the width adjusting spacer member 2 is two for example the two width adjusting spacer members 2 are connected by a connecting portion 23 where the two width adjusting spacer members 2 are connected indirectly to the connector 1 in other words the two width adjusting spacer members 2 and the connecting portion 23 cooperatively formed a substantially u shaped structure where the u shaped structure can be arranged selectively on the outer side of the connector 1 to provide further explanations when the width adjusting spacer members 2 are arranged on the outer side of the connector 1 the total width of the coupling mechanism will be increased otherwise when the width adjusting spacer members 2 are removed from.