K4 is missing, these make F mount tubes with different thickness as follows: More info > http://www.mir.com.my/rb/photography/hardwares/classics/nikonf2/macro/index1.htm K1-------------6mm K2+K3---------11mm K2+K3+K1------17mm K2+K5+K3------31mm K2+K5+K3+K1---37mm You can add PK-11A (8mm) to the above combinations!!