LaRue Tactical’s new VFZ are interesting. Instead out clamping horizontally they clamp vertically.

From LaRue …

VFZ is a new theory in the concept of clamping accessories to MIL-STD-1913 rails. Instead of using a horizontal cross-bolt, the VFZ uses a vertical bolt that draws up a clamping foot against the lower angle of the rail…seating the mount similarly to a fully-closed LaRue lever. Once installed on the firearm, index marks allow the user to remove the mount, then reattach to the same tension, providing unprecedented return to zero for a non-QD-levered mount. The unique vertical alignment of the clamp allows components that are structurally stronger than traditional cross-bolt designs.