Some surprising things happen as you move a project from BETA to production.  Suddenly all those various parts, that you hardly gave any thought to, become important.  Take machine screws for example.  When just building a few units for testing, you use whatever screws you have laying around, or shop your local hardware store.  But once in production, you need greater consistency for everything, including the screws.  So you head over to the Internet and call up sites that specialize in fasteners, and find to that unit prices are much less, but minimum quantities are much larger.  For example, the Centipede 416 uses 8, #2 screws, 1/2″ long.  Now that I have 5000 of those, I feel set for life, as long as I can remember where is am storing the 4500 I set aside  🙂