to loosen the locating member 76 to the unlocking position and then to rotate the handle 60 clockwise when the handle 60 is rotated clockwise as shown in fig5 the round rod 66 of the handle 60 is moved upwards along the first groove 334 of the l shaped groove 35 to carry the first stop plate 37 upwards along the vertical section 364 of the l shaped hole 362 to enable the index 374 to be aligned with the position point 368 b corresponding to 45 u00b0 angle and at the same time the handle 60 moves the sliding block 39 leftwards along the second groove 344 of the l shaped groove 35 to enable the flange 394 of the sliding block 39 to be moved from the right end of the elongated slot 382 of the second stop plate 38 to the left end of the elongated slot 382 thereafter the lever 76 is turned to the locking position to lock the handle 60 to the 45 u00b0 angle position if the operator keeps rotating the handle 60 clockwise as shown in fig6 the handle 60 moves the first stop plate 37 to the top side of the vertical section 364 of the l shaped hole 362 to enable the index 374 of the first stop plate 37 to be aligned with the position point 368 c corresponding to 90 u00b0 angle when the first stop plate 37 is moved to the top.