The Kastle Group FSM-DB is a Fortress Series optic mount, and this version is sized for 34mm tube diameters, so it matches optics built on that tube size. Kastle lists it as fitting most LRF platforms, which widens the range of optics you can choose from. The base uses a 1913 Picatinny rail interface, so it mounts to rails of that pattern.

The mount is machined from 7075-T651 aluminum and finished in black with a Type III MIL SPEC hardcoat anodize, a surface treatment applied to the aluminum. Kastle machines it in its own facility, drawing on decades of defense and aerospace manufacturing experience, and it is Made in the U.S.A. If your optic has a different tube size, the FSM-DB is also offered in 30mm, 35mm and 36mm ring sizes.

• Brand: Kastle Group
• Model: FSM-DB
• Fit: Fortress Series Optic Mount
• Tube Diameter: 34mm
• Rail Interface: 1913 Picatinny
• Material: 7075-T651 Aluminum
• Finish: Type III MIL SPEC Hardcoat Anodized, Black