RUSAN now make an incredible 2.5x Monocular to attach to most thermal imaging devices. The 2.5x magnification ocular already includes an adapter to use with Rusan's Modular Connectors - these are unit specific and come in various sizes.

Other than the 2.5x magnification ocular with included adapter, you would need the correct modular connector with the corresponding thread size for your thermal imaging unit.

These connectors are used with the RUSAN MAR connector required to mount the appropriate thermal imaging or night vision device.