Short answer, the 10L are thin. Best tool I've found for identifying certain hardware (since Van's just assumes you know what every bit is in a bag of 100 parts) is Google searching it in "images" on my iPhone. 95% of the time a picture will come up.
-10 approximately .063 thich, 10L approx .032. If you don't have them get a set of inexpensive dial calipers to measure just about anything except engine parts.
When I first started building it was confusing which was what on the different sizes all in the same bags. Once I was able to ID the washers I traced them on a sheet of paper for reference as the project progressed....kinda like they do at Aviation Depot for the cashiers. After a while I was able to ID them all by sight and the cheat sheet disappeared.
Section 5 of the paper work that came with the empennage on page 5-17 is a chart that gives the washer part#, inside & outside diameters and the thickness of the washer. I use my 6" caliper to measure them if I am unsure.
