Cube Corner Connectors enable for some custom Builds by creating among other thing a 3 way connection between Linear Rails or other Parts. 

It  can also be used to attach to the side of V-Slot Linear Rail to create a linear carriage.  The holes in the Cube Corner Connector are large enough to accommodate an Eccentric Spacer. This gives you the ability to create an adjustable Gantry cart that will lock onto like size V-Slot Linear Rail.

Product Features

• Can be placed along the length of the rail
• Can be stacked allowing expanded configurations
• Compatible with V-Slot and C-Beam Linear Rails

What is Included

• (1) Cube Corner Connector

Product Specifications

• 20mm x 20mm x 20mm
• Some applications may require low profile screws
• Anodized Aluminum
• Color: Black

Easy follow along assembly video - top notch awesome community support - open source files and documentation and examples.