Pinned Rectangular Frame

Step 1 of 5. Put the two 2x12 rails down flat, five holes apart.

Step 2 of 5. Lay a 1x7 beam across both rails, near one end. Turn it a quarter turn so it runs across the rails, not along them.

Step 3 of 5. Push four connector pins down through the cross beam into the rails underneath. Two pins into each rail. One pin per rail would let the frame pivot - the second pin is what makes it rigid.

Step 4 of 5. Repeat at the other end: one cross beam, four more pins.

Step 5 of 5. Check it. Hold two opposite corners and try to twist the frame - it should not move at all. If it racks, a pin is not seated. Press each one home until it clicks.