the plug p being made of a highly elastic material such as fiber reinforced plastics as best seen in fig6 a locker wall 13 projects from the bottom of the socket s whilst spanning the face side and back side walls 12a 12b of the socket s a center guide groove 14 is formed in the face side wall 12a running in the longitudinal direction of the socket s a leaf spring 15 having a center projection 15a is fixed at one end to the face side wall 12a in the guide groove 14 in the assembled state the plug p of the limb l is received and held firmly in the socket s of the handle riser h the plug p is provided at the bottom end with a locker cutout 17 engageable with the locker wall 13 in the socket s near the string side end of the plug p a first circular supporter piece 18 is fixed to the face side wall pa of the plug p by means of a set screw 16 this supporter piece 18 has a bottom brim 18a whose diameter is roughly equal to the width of the plug p and a thread 19 is formed in the periphery of the circular piece for screw engagement with an adjuster nut 21 the first supporter piece 18 further has a center projection 20 engageable with the center guide groove 14 formed in the face side wall 12a of the socket s the set screw 16 is received in the center axial.