Customizeable T-slot connector for 20mm or 30mm

You need to run the customizer to select length and size

This is best used with
http://www.thingiverse.com/thing:2320122
or
http://www.thingiverse.com/thing:2322889

Also use
https://www.thingiverse.com/thing:2330875
to join the opposite side to connect two t-slots together