Pagewidth printheads, for use in printing systems, are known.  Such printheads typically span the width of the print media on which information is to be printed, and as such the dimensions and configuration of the printheads vary depending upon the application of the printing system and the dimensions of the print media.  In this regard, due to the large variation in the required dimensions of such printheads, it is difficult to manufacture such printheads in a manner which caters for this variability. 
Accordingly, the applicant has proposed the use of a pagewidth printhead made up of a plurality of replaceable printhead tiles arranged in an end-to-end manner.  Each of the tiles mount an integrated circuit incorporating printing nozzles which eject printing fluid, e.g., ink, onto the print media in a known fashion.  Such an arrangement has made it easier to manufacture printheads of variable dimensions and has also enabled the ability to remove and replace any defective tile in a pagewidth printhead without having to scrap the entire printhead. 
However, apart from the ability to remove and replace any defective tiles, the previously proposed printhead is generally formed as an integral unit, with each component of the printhead fixedly attached to other components.  Such an arrangement complicates the assembly process and does not provide for easy disassembly should the need to replace components other than just the defective tiles be necessary.  Accordingly, a printhead unit which is easier to assemble and disassemble and which is made up of a number of separable individual parts to form a printhead unit of variable dimensions is required.