Geissele Magazine Well Reaction Block Grey. The armorer mounts the lower receiver to a workbench by sliding the Reaction Block into the mag-well then clamping the Block. The Vice Block provides an ultra-stable platform for performing an array of lower receiver operations from either the top or the bottom. Quickly and easily start your MLOK nuts utilizing the integrated slots or simplify the installation of a buffer tube assembly. This tool keeps both hands of the armorer free to work saving both time and frustration. Specifications for Geissele Magazine Well Reaction Block: Manufacturer: Geissele Fabric/Material: Aluminum Gun Model: AR-10 AR-15 Weight: 1.56 lb Color: Grey Package Contents: Geissele Magazine Well Reaction Block What firearm models does the manufacturer say Geissele Magazine Well Reaction Block is compatible with? The manufacturer says that Geissele Magazine Well Reaction Block is compatible with AR-15 AR-10Geissele 02-2781: Magazine Well Reaction Block Grey