The tilt rods are the thin pieces which are moved to control the angle of the louvers. The length needs to be just slightly longer than the distance between your top louver pin and you bottom pin. I like to leave 1/2" sticking out beyond the end louvers... so in my case the distance between the two pins was 30", so I made the tilt rods 31" long (1/2" on each end).
I prefer to make each rod 1/2" wide and 3/4" thick, however it is reasonable to make them 1/2" thick... it just depends on whether you want a thin unobtrusive tilt rod or a sturdy feeling thicker tilt rod.
You can easily make the tilt rods for both shutters (and several more) from a single board. Simply use the rip fence on the table saw to rip each side to the desired width and thickness.
The next step is to round off the outer edges of each tilt rod. I used the same 3/16" roundover bit, but you can adapt to your personal preferences. I only round the edges that will face the user... the two edges facing the window are left square.
The final step is to use a fastener of some sort that will allow the louver to pivot but still firmly fix the tilt rod to the louver. After some research and experimentation I found the cheapest and easiest way is to use strong staples. I bought this Stanley Sharpshooter staple gun from Home Depot. It has two depth levels. Neither of these will sink the staple all the way in... which is ideal. Each staple should stick out above the wood between 1/8" and 1/4". The matching staple on the louver will do the same and interlock with the other.
Mark each place on the tilt rod where a louver pin would hit and staple each spot parellel to the length of the rod. This is important... don't staple perpendicular to the length because this wouldn't allow the freedom of movement needed. You may notice the staples feel somewhat flimsy and as if they won't hold. To fix this I used a small dab of gorilla glue at each point where the staple touches the wood. After drying this will be sufficiently strong.
One last point. I didn't put in the staples until after I painted the tilt rod, but if you are careful it should still work to do it beforehand.