Fabrication of micro-devices for small bubble and droplet generation is usually tedious or costly. Here we present a simple capillary-assembled micro-device by modifying the capillary embedded step T-junction microchannel. Besides a capillary in the side channel, another same size capillary is placed at the downstream of T-junction. The two vertically embedded capillaries inherently guarantee the device symmetry by forming an arch orifice. And it could be applied to both L/L and G/L micro-dispersion with focused continuous phase flows. Monodispersed small bubbles of 35 mu m (CV = 3.52%) and droplets of 15 mu m (CV = 2.12%) are generated with stable flow-focusing jetting regime, by thin jets deriving from the large interface and arch orifice in the device. A general bubble and droplet size scaling law is obtained, and it could predict the bubble and droplet size very well. The device could provide a more convenient approach for adjusting bubble and droplet sizes than usual methods. The device shows its significant advantages of easy assembly, low cost and high versatility for both small bubble and droplet generation. (C) 2016 Elsevier B.V. All rights reserved.