All of the mono-block scope mounts have in common that both scope rings are made of one piece of material. Making a whole mount of one piece of raw material is usually possible by milling. These mounts are normally made for tactical applications, because they can be used in the toughest conditions. They are normally made out of one piece of hiqh quality aluminium alloy (like 7075T6), because steel might be too heavy for such applications. Steel is normally used only with the screws or claws that hold scope mount onto the Picatinny rail. However, there are some manufacturers which make nice mono-block mounts for hunting applications also (Spuhr, ERA-TAC Ultralight, etc.).
This type of mounts is suitable for use on Picatinny rails. Although, there are other rail standards that are known as common practice: 11 mm (AI), 16.5 mm (Tikka, Sako TRG), 19 mm (CZ 550)... They can be quick detachable or fixed (however, most of them are fixed).
ERA-TAC Ultralight Mount for Picatinny, 30 mm
Mono-block mounts for tactical rifles might be nearly perfect to use and main reasons for that can be found in:
They offer perfect ring alignment which is the key to not damaging or flexing your scope. Large contact surface between the scope and the mount might also be a favourable factor. Lapping during the process of mounting the scope is not needed. In addition, bedding is also not needed. All of the text above is true if we are talking about mounts of proper quality.
On the other hand, you have to be prepared for a (usually) bulky appearance and less adjustable length for proper eye relief.
Tactical mono-block scope mounts, made of high quality, normally have more than just one recoil stopper.
Some of the manufacturers (like Spuhr) advise their customers to oil surfaces between their mount and Picatinny rail before the mounting of them. They also advise to use resin between rings and rifle scope.
Spuhr Unimount for Picatinny, 35mm, 6 MIL 20.6 MOA
A lot of mono-block mounts offer additional attachment points on their rings. These attachment points are normally used for red-dots, lasers, rangefinders, angle indicators, etc. Bubble levels are also common on these mounts (on the rear side of the mount – Tier One, Spuhr,...). These bubble levels are aligned with the Picatinny rail under them.
Practically all of tactical mono-block mounts use 6 – 8 screws for tightening the scope. It is very rare for such mounts to use only 4 screws. With tactical mounts, rings are normally divided 50:50 (upper and lower part of the ring, tightened with screws), which is different than with other, for example hunting mounts, where rings are divided in different ratio – for example 60:40 (upper / lower part of the ring). In this case, upper part is bigger than the lower part, which in practice means that scope is embraced by the upper part of the ring a little bit more.
Tactical mono-block mounts are the most common mount form with inclination. If mounts are made with inclination, it is usually 10, 20 or 30 MOA. These type of mounts are great for long range shooting, because they offer a whole new possibilities for long range shooters. Majority of the mono-block mounts with inclination, is 20 MOA. However, there are mounts up to 70 MOA on the market (for example: Era-Tac from Recknagel).