EZ Mounts, for Installation of 3/4" Round Balusters on Stairs by Fortress
Made by Fortress Railing Products
Fortress Item # 640056
Each Package Includes:
20 Durable Nylon Standard Railing EZ Mounts (for stairs)
20 Stainless Steel Screws
Note that 2 EZ mounts are required per Baluster

More details including dimensions and features:
The diameter of the connectors is 5/8" and they are designed to fit into 3/4" inch round balusters.  Simply install the mounts onto rail and place Vintage Round Balusters over the mounts for fast installation.
- The mounts are hidden once the balusters have been installed. 
- Simplifies baluster installation.
- Protects and installs 3/4 in. vintage round balusters
- Allows for a quick and secure baluster to rail installation
- Eliminates the need for drilling holes in your rail material
- Protects balusters from treated lumber
- Prevents stains caused by condensation