In general, retainers may serve two purposes. If they are designed for retention, they hold the board in place. If they are conductive, they provide thermal transfer from the PCB to the enclosure. The extent to which they perform these two functions largely depends on the design of retainer chosen. Schroff offers a wide variety of Calmark and Birtcher retainers to meet the needs of many applications from economical nylon card guides, to Calmark Retainers and Birtcher PCB Tainers, followed by Birtcher Lok Tainers, and finally ruggedized high performance Card-Loks and Wedge Loks.