the printhead nozzle face 252 and media support 301 by rotating rotatable spacer 410 in one direction by 90 degrees to place the second contact face 413 into contact with anti rotation rail 383 or to decrease the nominal spacing adjustment between the printhead nozzle face 252 and media support 301 by rotating rotatable spacer 410 in the opposite direction by 90 degrees to place the third contact face 414 into contact with anti rotation rail 383 fig1 shows that rim 440 of rotatable spacer 410 has a first height near first contact face 412 but has a lower height near second contact face 413 and third contact face 414 as a result second notch 443 and third notch 444 each have one tall wall and one short wall 449 while first notch 442 has two short walls 449 in this embodiment the tall wall of second notch 443 serves as a first stopper 447 that prohibits rotation of rotatable spacer 410 beyond the second notch 443 as will be described below similarly the tall wall of third notch 444 serves as a second stopper 448 that prohibits rotation of rotatable spacer 410 beyond the third notch 444 fig1 17 show perspective views of a portion of carriage 200 and a lockable adjustment mechanism 450 for locking a selected contact face into position in order to adjust a distance d between the printhead nozzle face 252 and media support 301 with reference to fig7 according to an embodiment of the present invention lockable adjustment mechanism 450 engages with a locking tab 435 and.