screw length ?

You don't "need" tubes if you don't want them. I have run my car with and without tubes, works fine both ways....and yes, I had rim screws with both. I always put a small dab of clear silicon on the screws before installation, then wipe off the excess. No real problems with leakage, one of my tires looses about 1 pound of air every 2-3 weeks...the other tire take about 2 months to loose 1 pound of air.

If you want tubes here you go....but they aren't cheap (65 bucks each):

http://www.summitracing.com/parts/mtt-9553