lockable into rotated positions 149 through 159 which are in 20 degree arcuate increments along the entire 180 degree arcuate travel 150 of arm 30 the arms may be locked into any incremental arcuate positions and such locked positions may be of any selected incremental size or degree and may be incrementally the same or different from each other in the embodiment shown the locked positions are enabled by bushings 270 which are stationarily attached to frame uprights 160 170 having incrementally spaced apertures 149 a 151 a et seq fig1 which correspond to angular positions 149 159 fig2 apertures corresponding to positions 153 159 not labeled shown in fig1 a pin 181 fig1 4 which is spring 282 loaded and mounted on rotatable axle flange 300 fig1 is manually insertable into any of the apertures e g 149 a 151 a in the flanged portion 270 of cylindrical bushing 272 the apertures in flange 270 corresponding to positions 149 159 by manually pulling backwardly on the head of the pin 181 releasing the pin and allowing the pin to be spring 282 force inserted into a selected aperture thus locking the rotation position of the rotatable axle 301 around axis 50 into a selected angular position as shown in fig4 the forwardly extending arm 20 with end portion 24 is pivotably attached at pivot axis 42 to bracket 23 which is in turn fixedly attached to or integrally formed together with the flange portion 300 of the rotatable axle.