102 u2033 of unequal length with appendage 102 u2032 being shorter than appendage 102 u2033 fig1 depicts insertion of t shaped projection into an opening 26 fig1 illustrates use of tool 92 to remove the cartridge from the housing and fig1 illustrates use of tool 92 to insert the cartridge into the housing the distinctions between use of the tool for cartridge insertion and removal lies in the cooperative engagement of appendages 102 u2032 and 102 u2033 in openings 26 specifically when the cartridge is to be removed from the housing it is desired that there be a greater surface engagement between the tool appendage and the undersurface designated by indicium 77 of flat center portion 76 this extended surface engagement is provided by larger appendage 102 u2033 for insertion purposes however appendage 102 u2032 is needed only for a minimum locking between the tool and the cartridge inasmuch as the insertion force is defined by contact between tool surface 100 and cartridge flat center portion 76 to assure a firm engagement of tool appendages 102 u2033 in particular with flat center portion 76 of cartridge top wall 74 an interlock is formed between appendages 102 u2033 and undersurface 77 of center portion 76 this interlock is provided by downwardly extending protuberances 77 a on undersurface 77 and upwardly extending protuberances 104 on appendages 102 u2033 when appendages 102 u2033 are moved to their positions as depicted in fig1 a locking engagement is effected between tool 92 and cartridge 22 to resist unintentional disengagement of these parts in operation and with.