special bolts?

Of the 5 bolts (per side) that hold the rocker arm rail down (sb) there are 2 bolts on each side with a small hole drilled through the head of the bolt. What is the purpose of these bolts? I guessed at first it was something to do with the oiling, but I don't know how if that's true. When I took the heads apart the bolts weren't used in any order I could tell....I think three with the holes were used on one side and 1 on the other. When I put it back together I used them in the holes one in from each end.....just seemed right to me.