Aluminum Attachment Blocks - $9.99 / 12 pack
Our new Attachment Blocks make it easy to join two flat panels at a 90 degree angle.
Constructed of 6061-T6 aluminum, these threaded blocks are extremely rigid and strong.
Each block has two 6-32 tapped thru holes.

Attachment Blocks are perfect for 90 degree mounting applications.

These blocks use 6-32 screws (not included).
http://www.servocity.com/html/attachment_blocks.html