Convert 11 mm Dovetail to 21 mm Picatinny Rail: 4.31 Inches length at the base, picatinny rail extends 6.1 inches / 155mm allowing for more flexible optics placement. Mount Base with Middle V-cut: Fit 11 mm dovetail mounts, Base mount 3/8" to 7/8" converter adapter. Low profile 0.54" riser rail for scope mount. Item weight: 3.74 Oz/pcs. Top With 14 Slots Picatinny Style Rail: Top 21 mm picatinny rail allows for the mounting of standard picatinny scopes or other accessories. Precision Material: Premium out of aircraft grade aluminum alloy and black hard coat anodize finish, sturdy & durable Complete with one vertical stop pin and 4 fixing screws with steel material. Easy To Install: Rail adaptor installs easily via dovetail mount and one vertical stop pin, attached allen wrench can help you to tight stable and no shaking.