The NXT-3R TM Reader usually designed for mounting on metal window mullions is one of the smallest on the market yet offers exceptional read range. Measuring just 3.75 inches high by 1.60 inches wide by .625 inches deep (9.5 cm high x 4.1 cm wide x 1.6 cm deep), the NXT-3R is one of the smallest proximity readers on the market. It is designed to mount directly on 4Xmetal or a wall with out mounting brackets or spacers.