Hawke Adapter Base 3/8" (Rifle) with Elevation to Weaver 5.4"/137mmHawke Sport Optics Universal Weaver Base allows you to mount Weaver style accessories to your firearm. Designed to firmly hold the scope in position. Perfect for converting a 3 8" standard rail to a Weaver rail. Having the extended rail allows for scopes or red dots to be mounted further down the barrel for that perfect eye relief. Mounts to 3 8" or 9 11mm rails Overall length: 5. 4 137mm Weight: 3. 9oz 110g Ideal for rifles, shotguns, or crossbows.