The print head unit includes {TAIL ~ a first print head} , a second print head , a third print head , and {HEAD ~ a print head frame}  
The print head unit includes { TAIL ~ a first print head } , a second print head , a third print head , and { HEAD ~ a print head frame }
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH