Cellular enabled Opengear devices (i.e. those with -Lx or -Gx in their full model name), all use a 2FF "Mini" SIM card. The Mini SIM card is 25mm x 15mm, and is depicted below:
If your carrier has provided you with a 3FF "Micro" or 4FF "Nano" SIM card, these can be put into an adapter for use in the Opengear device's SIM card slot. Take extra care when using an adapter that the SIM is securely in place.
The following depicts Verizon Mini SIM snap out from a Full Size template: