XCP dental x-ray film positioning devices help to increase the dimensional accuracy of dental x-ray images. (XCP stands for "extension cone paralleling." Some dental assistants refer to them as "Rinn" devices, after a company that manufactures them.) The XCP device has a collimator ring that is parallel with the film-holding plane of the x-ray film holder. This positioning helps an assistant to align the plane of the unseen, intraorally located x-ray film parallel with the plane of the cross section of the x-ray beam. XCP devices also help to prevent dental x-ray film cone cuts, since the extraoral collimator ring helps to indicate the boundary of the unseen x-ray film. Unfortunately, the devices can be confusing to assemble because each device consists of three pieces that can be assembled in multiple ways, and there are three types of such devices for anterior, posterior and bitewing radiographs (in addition to a fourth accessory device for taking endodontic radiographs). It can be challenging to determine which piece goes with which type of XCP, and to choose the correct XCP assembly for taking a desired x-ray. This article describes some clinical techniques of assembling XCP radiographic film-holding devices, describes the clinical use of XCP devices, and ways of overcoming intraoral obstacles to device placement.