Order them from ZAC.  You might pay a few extra bucks but in the run will save you a ton of headaches tying to source exactly the right nut, bolt and washer.  When you finish the the project you will never  it again.

If you are concerned about them being a little short go up one size.  It won't hurt anything.  I used what came with my kit though.  I don;t remember a counter sunk washer but that doesn't mean it wasn't there.  However, all bolts were long enough with about 2 threads sticking out of nut after torquing.

Steve

hi ernest i too at the beginning had the death grip it will ease up as you get use to flying i also added a arm rest so your arm doesnt tire..keep flying it will get better... joe

ernest what engine are you running? im running a corvair.you have to keep flying even for 20 min at a time.untill you feel comfy with the engine and airplane the hardest to get use to is when its bumpy you over compansate that will take time then you get above it then its smooth sailing then you will start to fly farther and higher. it will come  all the best  joe in fla..