The 40 mm main tube diameter is one of a kind, found only with the Romanian rifle scope manufacturer IOR. Why they have decided to make the tube so wide? Maybe it is easier for them to fit all their technology inside and to get extreme elevation range. Never the less the scope is massive and so are the mounting rings. Like with all other tube diameters there is one main thing to keep an eye out when mounting – the proper torque. Go over the torque value and the rifle scope is damaged. Go under and it will not be sturdy enough for a good, precise shot. The torque value should be monitored and done with a purpose made screwdriver. Do not exceed 2.2 Nm. The rings are made by: Rusan, IOR and Contessa.