Summary form only given. Investigations aimed at improving crystal unit characteristics over the range 400-1000 kHz resulted in designing quartz crystals operating in a double-shear mode. The investigations were realized on the base of quartz crystal bars having a rectangular cross section of close cross sizes, with length being along X-axis. Vibrations of such bars may be approximately interpreted as a superposition of two shears-in thickness and in width of the piezoelements. Crystal units operating in the above mentioned mode have high electrophysical parameters: dynamic resistance 5-100 Ohm, motional inductance 2-20 H, quality factor 10⁵-2×10⁶, capacitance ratio up to 350, high temperature-frequency stability and low aging. Calculation results showed that quartz crystal units may have high temperature stability by changing the cut angle and dimensions of the piezoelements.