The 34mm main tube is somewhat a new standard meant for tactical rifle scopes. It is adopted by a lot of rifle scope manufacturers as it provides more space for elevation compared to the 30mm tube. In order to mount the 34mm rifle scope, you need the 34mm scope rings to fit this diameter.
The most important thing when mounting a rifle scope with 34mm scope rings is to be aware of the pressure needed to fasten the scope rings. Go over the limit and the structural integrity of the rifle scope will be compromised. Scope rings can also leave a visible mark if not tightened accordingly. The amount of torque should not exceed 2.2 Nm.
34mm scope rings are usually at least 20mm wide, while with tactical scope rings mount the width can be as much as 32mm mounting scope rings.
A lot of different manufacturers are putting their 34mm scope rings mounts on the market.
MAKuick One-piece Mount, Tikka T3, 34mm scope rings,
EAW 34mm scope rings
MAK 34 scope rings
Rusan 34 scope rings
Recknagel 34 scope rings
Contessa 34 scope rings
Spuhr 34 scope rings
Henneberger 34 scope rings
Kozap 34 scope rings,
Leupold 34 scope rings
Lapping is a process that is essentially lining two 34mm scope rings perfectly to one-a-another. It is done with special cylinders that grind off the excess metal.
In the worst-case scenario, the axis that runs through the center of the rear ring does not completely match the axis that runs through the center of the front ring. For this reason, the scope, if mounted into such scope rings is under unwanted structural stress. The most obvious problems that occur due to this reason are less than perfect optical performance, tracking problems, the side focus mechanism can stop working and the point of impact groups can be dispersed.
If the ring is designed in the fashion of 1/3 base of the ring and 2/3 of the top of the ring then lapping is not required as the design is plastic enough to bend slightly and adjust its shape to the scope tube. The same applies to ½ - 1/2 scope rings mounted on the single-piece base.
It may be a good idea to take into consideration to choose the 1/3: 2/3 scope rings as they do not require additional lapping to be fitted properly. Or use a single-piece mounting base.
Lapping is also not required with monoblock mounts and all mounts are made from one piece of material and alignment of both 34mm scope rings is usually perfect. It is also not required with high-quality European mounts since their tolerances are minimal.