The 4 hole - 90 degree angled flat plate is an external fastening method that requires no machining services. This flat plate creates a 90 degree angle between profiles and its shape reinforces the strength of the connection. It is a durable option that is easy to assemble and can be reconfigured and reused. The suggested mounting hardware can be found on the "Suggested Hardware" tab. Tip: Use double or triple slide-in economy T-nuts to save time and money. Pre-load your hardware prior to connecting profiles to simplify your assembly.