Ensure you did not accidentally download the extensions for Revit 2017 or 2019. Extensions are strictly version-locked to their specific yearly release and will not function across different versions.
If your account does not show legacy add-ons, your organization's Contract Manager or BIM Administrator may need to assign the product permissions to your user profile. Download Revit Extensions for Autodesk Revit 2018
If prompted by Windows User Account Control (UAC), click Yes to allow the installer to make changes. Ensure you did not accidentally download the extensions
Before Autodesk integrated advanced steel connections directly into the core Revit properties platform, this extension was vital. It provides access to parametric steel joints, including base plates, gusset plates, and frame connections. 3. Timber Framing Extensions including base plates