ClikRay X-Series Bite Blocks fit thinner sensors such as Apex Dental Sensors, XDR, Original Schick, Progeny, Quickray, Dentimax and Dent-X. Precise Fit holders are available in size 2 blue holders and size 1 yellow holders. ClikRay X-Series bite blocks are colored according to their sizes so choosing the appropriate sized holder is easy. No more confusion!