This spacer set is for use with the X-ray Chassis in conjunction with the 3 spacers that are already included with the chassis. There are three spacers in the kit along with mounting screws which increase the length of pull from 3/8" to 1 1/8" beyond what the included spacers give. With all three spacers in this kit and all three that are included with the chassis, LOP will be approximately 15".
Big Book Catalog, Issue:72, Page:185
Sinclair, Issue:5B, Page:238