Opto-mechanical mounts can cause significant distortions to monochromator crystals and mirrors if not designed or implemented carefully. A slope measuring profiler, the Diamond-NOM [1], was used to measure the change in tangential slope as a function of crystal clamping configuration and load. A three point mount was found to exhibit the lowest surface distortion (< 2μrad peak-to-valley) over the whole length of the monochromator 2nd crystal. A thermal circuit, comprising the liquid nitrogen manifold to the crystal, was modelled using experimental data for the 2nd crystal absorbed beam power and braid link thermal conductance. In the case of the I09 monochromator 2nd crystal assembly, the temperature drop across the 3 indium mount pads was calculated to be 25% of the total 0.22 K. Less than 1% loss of flux due to the 2nd crystal strain is expected at 25keV. This three pad mount will be used in the monochromators on the I09 and I23 beamlines at Diamond Light Source.