Hi Grade 7 - 3mm diff balls. 12 in pack. Tamiya cars are the favorites, Durango cars need 14 so please look at other listing, and other diffs using 3mm diff balls For your reference: ABEC 1: 0.0075mm (0.000295") is the most crude, the least precise, and the cheapest ABEC 3: 0.0050mm (0.000197") is what is mostly know as cheap and normally associated with China. Won't roll very smoothly or fast. ABEC 5: 0.0035mm (0.000138") these are the normal grade that the majority buy and what normally one finds on the market but ABEC 7: 0.0025mm (0.000098") would be very fast and smooth, but very expensive. Although extremely rewarding in RC and very long lasting, there is a risk of needlessly damaging them if you over tighten your diff. ABEC 9: 0.0012mm (0.000047") The higher grade and ridiculously expensive