George Miller's  "Three Card Burr"

Three cards interlocked along three axes to form three intersecting planes. Assembly requires that the cards are bent and stressed quite a lot. Once assembled, the cards "lock" into place and disassembly is a next to impossible task. 

Inspired by George Miller's "Three Card Burr".

Template
Here's a PDF template that should print the card outline at the proper size. (Make sure scaling is 100% when printing.)

Assembly
It's a puzzle and there are only three pieces. Figure it out!