ORIGINAL: 72
I tried every way you can think of to keep the bolts tight, including locktite and finally tried whats in the picture. This now works fine. The props and spinners were balanced and I still could not keep the bolts tight until I went to this.
You're probably using 10-32 screws. Use 5 mm in stead and heat-resistant thread locker available from your local Advance Auto Parts.
Attached about 100 flights of abuse.