The internal mechanisms may comprise {TAIL ~ a wide variety} of actuation systems for extending and retracting {HEAD ~ the writing implement}, including a cam actuation assembly, an edge slide actuation assembly, a gravity actuation assembly, a pressure actuation assembly and a push button actuation assembly 
The internal mechanisms may comprise { TAIL ~ a wide variety } of actuation systems for extending and retracting { HEAD ~ the writing implement } , including a cam actuation assembly , an edge slide actuation assembly , a gravity actuation assembly , a pressure actuation assembly and a push button actuation assembly
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH